CHAPTER 2: LITERATURE REVIEW

2.1. WHAT IS A YELLOWFISH

Cuvier and Cloquet (1816) has long held the huge genus Barbus to be a major problem for ichthyologists. Until recently yellowfish formed part of the Barbus group, which is one of the largest fish genera in the world. About 50 species in South Africa were classified under this genus, which included minnows/barbs and yellowfishes. This made it the largest genus in South Africa. Above- mentioned groups forms part of the family Cyprinidae with the following characteristics: Cyprinids are primary fresh water fishes, with a wide range of sizes, shapes, life history styles and habitat preferences. They lack teeth on the jaws, but have strong pharyngeal bones with teeth. They also lack a true stomach, especially in the detritus and plant feeders where the gut is extended and convoluted. Normally cyprinids are strong swimmers and some are distinctly modified to live in strong currents. The males may differ from females in having longer fins, brighter breeding colours, and in some instances tubercles on the head, body and fins. Cyprinids is an extremely large family with about 275 genera and more than 1600 species originating from Africa, Europe, Asia and North America (Skelton, 2001).

A determined effort to resolve this taxonomic deadlock has been made in recent years following the development of modern genetic analytical methods and breakthroughs in understanding relationships in karyological data (Mulder,1989; Skelton, 1993, 2002 & 2003). Oellermann and Skelton (1989) revealed that unlike minnows the southern African yellowfishes have a hexaploid karyotype of around 150 chromosomes. Furthermore, these yellowfishes grow to a large size and live for may years, and have scales with longitudinal or parallel striae and the primary dorsal ray is usually spinous. These species are extremely variable in shape and appearance, even within the same population, and this caused considerable confusion (Skelton, 2003). This is particularly true of the mouths and the lips, which may be thin and firm or thick and fleshy. It took several decades to realize that the mouth structure and other features of these fishes were very “plastic” and therefore unreliable characteristics to identify and delimit a yellowfish species (Skelton, 2003). Three forms of mouth and lip shape are recognized: the normal u-shaped mouth with moderate lips, a straight-edge mouth with horny lower-lips, and thick, fleshy (rubber) lips. Lip development

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Reproduction Strategy Of Labeobarbus Polylepis (Smallscale yellowfish) can be related to feeding habits and can therefore change from normal to thick depending on habitat and food sources.

Several other studies confirmed that the other large parallel striated scaled African Barbus species were also hexaploid and genetically distinct from the tetraploid (from around a 100 chromosomes) European barble group species. It was argued that the African yellowfish species can be recognized as an distinct lineage at the generic level and also that all other Afro-tropical Barbus should as an intra-measure be placed in a taxon called Barbus until a taxonomic analysis determine their systematic position. According to Skelton (2002), the large African hexaploid Barbus lineage has most recently been considered within the subgenus Labeobarbus Rüpple (1836). On the strength of these arguments presented and the phylogenetic relationships, it was opted to elevate the earliest available generic synonym for the large African hexaploid yellowfishes, that is, Labeobarbus Rüpple (1836), to full generic status. The new taxonomic changes of all the species of large yellowfishes within South Africa as proposed by Skelton (2002) are presented in Table 2.1. Also in the table are new common names, which included a geographical component as strongly advocated by the Yellowfish Working Group of the Federation of South African Flyfishers (FOSAF). This working group advocated strongly that by attaching the geographical element, greater caution will be exercised in not translocating these species beyond their natural range and this is important for the conservation of the genetic integrity of these species.

Table 2.1. New taxonomic changes of all the species of large yellowfishes within South Africa

Species New Common Name Old Common Name Labeobarbus aeneus Vaal-Orange smallmouth yellowfish Smallmouth yellowfish Labeobarbus capensis Clanwilliam yellowfish Clanwilliam yellowfish Labeobarbus kimberleyensis Vaal-Orange largemouth yellowfish Largemouth yellowfish Labeobarbus marequensis Lowveld largescale yellowfish Largescale yellowfish Labeobarbus natalensis Kwazulu Natal yellowfish Scaly Labeobarbus polylepis Bushveld smallscale yellowfish Smallscale yellowfish

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2.2. THE LARGE YELLOWFISH SPECIES OF SOUTHERN AFRICA

The yellowfish species Labeobarbus kimberleyensis, Labeobarbus aeneus, Labeobarbus natalensis, Labeobarbus capensis and Labeobarbus marequensis, is collectively known as the large yellowfish species. This group has received a large amount of attention from conservation authorities, universities and anglers. Labeobarbus polylepis has received comparatively little attention and relative little is known of their ecology and breeding behaviour.

2.2.1. Labeobarbus Natalensis Description The dorsal fin is IV, 8-9 and the anal fin is iii,5. The dorsal fin originates in front of the pelvic and the primary ray may be flexible or spinous. The scales are in a lateral line 35 – 39, but usually 36 with 14-18 around the caudal peduncle. The mouth form varies extremely from a straight scraping form to enlarged “rubber lips” with well-developed barbles (Skelton, 2001).

Distribution Labeobarbus natalensis is endemic to Natal and is widespread throughout the province from the Mkuze River southwards to the Umtamvuna on the Eastern Cape border.

Habitat & Ecology Labeobarbus natalensis is primarily a river fish, but will also occupy dams where they may grow unusually large. In rivers they are found in both pools and rapids, but the larger fish are seldom found in water less than 30 cm deep (Coke, 1997). Furthermore, this species are shoaling and non-territorial, and both juveniles and adults stick together in shoals, the young often favouring warm shallow backwaters. Upstream migrations occur in spring with the onset of rain, most of the migrations occur at night, but daytime migrations may also occur and hundreds of fish may be seen attempting to scale a waterfall. Many of these migrating fish are juveniles and so the migrations cannot be truly described a spawning runs. In winter scaly’s are known to migrate downstream when water temperatures in the headwater regions are low (Crass, 1964). Scaly’s are opportunistic feeders and plant material such as filamentous algae, diatoms and organic detritus may at times pre-dominate in the stomach contents, or else insect larvae may form the bulk of the food. Small fish feed mainly on midge larvae and mayfly-nymphs whereas larger fish are fond of crabs.

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Breeding behaviour Males reach sexual maturity at one year whilst females reach it at two years of age. Males as small as 105 mm (FL) have been recorded sexually mature, whereas females do not mature until they are bigger than 140 mm. A female of 1.4kg may contain over 20 000 eggs. The peak spawning period is November and December (Crass, 1964), but spawning activity has been recorded as early as September. Breeding takes place in running water on well aerated, algae free gravel or cobble beds, and spawning starts when the water temperature rises above 19ºC. The spawning event is described as a number of fish ascending into the riffle, where the water can be so shallow that their backs and dorsal fins protrude out of the water. Several male fish gather close around a female, nudging at her flanks and thrashing their tails. During this activity eggs and sperm are released into the water (Coke, 1997).

Artificial spawning Wrigth and Coke attempted to artificially propagate Labeobarbus natalensis, and made preliminary observations on the early development on this indigenous fish species. These studies were undertaken at the Natal Parks Board Hatchery at the Royal Natal National Park in the Drakensberg.

Naturally stimulated, ripe running, Labeobarbus natalensis were collected on spawning beds in the Bushmen’s River between October and November. These fish were transported to pre-prepared 0.125 ha earth dams with artificial spawning beds according to the design of Le Roux (1968). Additional to drain pipes that ensure downward flow of water through the gravel, vertical pipes were constructed to create a horizontal flow of water both through and over the gravel beds. Success was limited as only a few (50) developing ova and twelve days later, approximately 20 fry were collected. Of importance was that these tests demonstrated that Labeobarbus natalensis could be conditioned to spawn over artificial gravel beds. Under normal conditions Labeobarbus natalensis select fast flowing water on spawning beds and spawning takes place predominantly at water temperatures higher than 19 °C.

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Several variations of the dry stripping techniques were tested on ripe running fish collected on the natural spawning beds in the Bushman’s River. From the comparison chart of the different dry stripping technique variations, it is clear that fertilization is only successful within a short period after stripping. Furthermore, delays and interference by fluids such as water, body mucous and urine, hinders the process. The authors further predicted that ova only remain receptive for fertilization for 15 seconds after contact with water. The natural adhesiveness of the eggs caused clumping, but this can be reduced by rinsing with water after fertilization. As ova become too sensitive to handling about 10 minutes after fertilization, the authors recommend handling to be completed within this time period. Also, fertilized ova can be briefly handled four days after fertilization without ill effects. The results also indicate that waterflow over the fertilized ova facilitates their survival and the greater the waterflow efficiency the greater percentage survival rate. These tests with the use of artificial spawning beds indicate that this technique is partially successful in propagating Labeobarbus natalensis, but requires considerable further investigation and refinement (Wright & Coke, 1975a).

Wright and Coke (1975b) provided the first and only description of the early development of this indigenous fish species. The development of larvae and fry over a period of 68 days under hatchery conditions was documented through superficial verbal descriptions of the events, and no photographic evidence of the embryonic development was documented. No mention on the methodology or apparatus used during embryonic development was made.

Wright and Coke (1975b) recorded the development as follows: Swollen Labeobarbus natalensis eggs (2.5 mm in diameter) were kept in wire mesh hatching trays suspended in troughs through which a constant supply of water flowed, varying in temperature from 15.5 °C – 22 °C. The mean maximum water temperature was 17.9°C. • Day 3: at 66 hours after fertilization the transparent developing embryos could be discerned • Day 4: at 89 hours the first physical movement of the embryos were observed. • Day 6, 7 & 8: hatching occurred over a period of three days, and the overall length of the embryo was 8.5 mm. Immediately upon hatching, the larvae started a burrowing activity, which lasted for a couple of days – the direction of this is negatively phototropism.

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• Day 13-17: Wright and Coke (1975b) described in detail the start and the effect of the gas bubble in the air sack, and the re-orientation and buoyancy of the larvae. • Day 65: The overall length of the fry is between 9 – 10 mm, representing and increase of 6 – 12% (0.5 – 1.0 mm) in 60 days. As water temperature affect the larval development rate the low temperatures experienced at the Royal Natal Hatchery would have resulted in slower growth rates.

2.2.2. Labeobarbus Aeneus Description The dorsal fin is D IV, 7 - 9 and the anal fin is iii,5. The dorsal fin originates behind the origin of the pelvic fin and the primary ray is stout and spinous. The scales are in a lateral line 36 – 44 usually 40. The mouth is subterminal to inferior with extremely changeable lips varying from thin and firm forming a scraping edge, to moderate or very thick (rubber lips). Juveniles are silvery in colour with dark blotches. Adults are a golden olive bronze colour.

Distribution Smallmouth yellowfish, Labeobarbus aeneus is endemic to the Orange-Vaalriver system. However, the Department of Nature Conservation (TPA) translocated this species to the Gouritz (1953), Kariega (1963), Tsomo (1964) and Olifants rivers (1961) (Skelton, 2001).

Habitat & Ecology Labeobarbus aeneus is an omnivore with a relative gutlength value of 170%, which is typical for omnivores, also the “rubberlips” is an adaptation to an omnivorous feeding behaviour.

Breeding behaviour In Labeobarbus aeneus, males reach sexual maturity at ± 28 cm and females at ±34 cm , at an age varying between 4 and 5 years. The females also grow larger than the males (Mulder, 1971). This corresponds with the observations of Groenewald (1957) whom did egg counts for a Labeobarbus aeneus female measuring 32.5 cm (TL).

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Looking at gonad development it appears that Labeobarbus aeneus breeds early in summer from October to November. Also, the egg production increase gradually with size increments to about 44 cm (TL), after this stage (44 cm (TL)) the egg production becomes more or less constant. According to Mulder (1971), egg production ranges between 30 000 to 40 000 for females varying between 44 – 53 cm (TL).

Artificial spawning Le Roux (1968) designed the Labeobarbus holubi experimental propagation trails based on observations by Groenewald (1961). Groenewald noted that Labeobarbus holubi deposit the ova in nests excavated in gravel beds. In the process, the tail fin is used to remove fine particles with a fanning motion. The completed nest was roughly 12 – 18 inches in diameter and slightly concave. Also, spawning started as soon as water temperatures during spring exceeded 65°F. In addition, it was observed that this yellowfish spawn throughout the summer, as fry were noticed as late as March. Thus, accordingly artificial gravel spawning beds were built in dams for the culturing of Labeobarbus holubi. Le Roux (1968) describe in detail the construction of these artificial gravel spawning beds and emphasised the importance of having a constant flow of water through the beds, as ova may suffocate from lack of oxygen if the water supply is interrupted. Thus, environmental cues were used to try and manipulate Labeobarbus holubi to spawn on the artificially created spawning beds. The actual spawning event was never observed, but eggs in an early stage of development were collected in the morning. This would imply that spawning occur during the night or early mornings. The observed eggs were located in a deposition in the gravel, and covered with available material. Some of the eggs were found under 6 inches of gravel. The collected (transparent and slightly pinkish) eggs were spheroid or slightly ellipsoid in outline with a diameter of approximately 3 mm.

The development of the fertilized eggs is relatively fast: • Day 1: (24 hours) movement of embryos can be seen. • At the 3rd day, the embryos are clearly formed with poorly developed fins. The onset of cardiac pulse was noted. • Day 4: hatching occurs with an embryo of 8.5 mm long. At this stage the little fish is still undeveloped with no mouth, undeveloped gills with an unpigmented body. For some time

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after hatching, the embryo cannot lead and independent existence, until the mouth is fully developed, it has to live on the yolk sack still attached to the abdomen (Le Roux, 1968). • Day 5: young fish starts to swim-about actively • Day 14: fry is seen to form schools in the shallows among the emergent weeds. • Days 120 – 180: the young fish reaches a length varying from 3 – 4 inches.

2.2.3. Labeobarbus Marequensis Description The dorsal fin is D IV, 8-10 and the anal fin is iii, 5. The dorsal fin originates in front of the pelvic and the primary ray may be flexible and the height is extremely variable within the population. The scales are in a lateral line 27 – 33, 12 around the caudal peduncle. The mouth is sub-terminal with extremely variable lips with two pairs of barbles. In both sexes small tubercles develop on the top and sides of head, as well as on the anal fin rays. Colour varies according to water clarity, from pale olive green (turbid water) to bright golden yellow (clear water). Juveniles are usually silver, and blotched with dark specks (Vlok, 1997).

Distribution This species is widely distributed from the middle- and lower Zambesi River and south to the Pongola River system. Larger specimens occur in the Lowveld rivers below the 600m altitude (Skelton, 2001).

Habitat & Ecology The fish prefer running water of perennial rivers, but also occurs in impoundments, although this is not a preferred habitat for largescale yellowfish. Gaigher (1973) regards it as an unspecialised species with a wide distribution that occurs in the Limpopo River system in pools and rapids of perennial streams at all altitudes.

The fish feed on a variety of organisms that include plant material, algae, insects, snails, prawns and small fish. The size of the food will be determined by the size of the mouth. During a study in the Njele dam on the diet of Labeobarbus marequensis it was found that the contents of stomach analysis revealed 51.2% plant material and 34.5% animal materials. This single study suggests

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that the largescale yellowfish is omnivorous (Saayman, 1986). The mouth forms Varicorhinus –type lips suggesting that the hard, chisel type lower jaw is used to scrape algae of the rocks, but can also be used to dig for insects and larvae in sandy bottoms. Once again, various authors (Crass, 1964; Pienaar, 1978 & Skelton, 2001) has indicated that the diet of this fish consist of algae, plant detritus, the larvae and adult stages of aquatic insects, snails and even small fish. Stomach content analysis by Fouche et.al.(2003) of a variety of length classes (31 – 110 mm) has shown that Labeobarbus marequensis feed primarily on algae and detritus and invertebrates form a very small component of the diet. However, as the fish increase in size, larger volumes of insect residues are found in the stomach contents, which indicate a possible shift towards a more insectivorous diet. The increase in stomach volumes and the accompanying relative length increase in the stomach support this. As far as habitat preferences are concerned all size classes do seem to prefer the shallower less than 0.5 m areas.

In a study by Hecht (1986) in the Nwanedzi/Luphephe dams, both “rubber lips” and “ thin lipped” varieties were found in the dams at approximately 1:1 ratio. This is an opportunistic feeder that is primarily a plant material feeder (herbivore), but will also take animal material when available.

Labeobarbus marequensis is a slow growing, warm water cyprinid with an extended breeding season. The growth rate of Labeobarbus marequensis differs from different geographical areas and different dams. It appears that this can be correlated to water temperature and food available (Ferreira, 1972 & Potgieter, 1974). Labeobarbus marequensis from Roodeplaat Dam reveals faster growth rates for the first five years. Thereafter from the age of five years onward, the growth rate is more or less the same in the Incomati-Limpopo river systems and Lebowa impoundments (Saayman, 1986).

Breeding behaviour Sexual maturity was determined for males and females and results indicate that sexual maturity is at a relative late stage, and that females mature at a greater age and length than males. Once again, this differs from different river systems (Gaigher, 1969; Batchelor, 1974; Potgieter, 1974 and Saayman, 1986). Females grow faster than males, and they also attain sexual maturity (50%) between 290 –310 mm (SL) at an age of between two and three years. Males attain sexual

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maturity (50%) between 180 – 220 mm (SL) at an age of between two and three years (Hecht, 1986). The male to female ratio in the Nwanedsi/Luphephe dams was calculated at 1:1.52. Gaigher (1969) found the females of this species from the Incomati/Limpopo river system to mature at a minimum length of 28 cm (FL) and males to mature at 12 cm (FL). Batchelor (1974) found males from the Doringdraai Dam to mature at 17 cm (FL) while the females reached maturity at 28 cm (FL), while Potgieter (1974) found males to mature at 15 cm (FL) and females at 22 cm (FL).

Once again, the determined breeding season also differs from author to author and different river systems. Data from Nwanedsi/Luphephe dams indicates that this species have a relatively long breeding season from October to late February (Hecth, 1986). While Gaigher(1969) found the breeding season for this species to extend from September or October to January or February. Potgieter (1974) found the breeding season to extend from August to February. Ripe and running females were first sampled during October and in December spent females were found. While during middle January the majority of the females were spent with a few still in the ripe and running stage (Hecht, 1986).

It seems from all the investigations done that there is a definite breeding peak during the late spring early summer months, depending on the rainfall, with a smaller less prominent peak in January or February.

Fecundity analysis of this species done in the Lebowa impoundments, has shown that this species can produce up to 41 800 eggs in a ripe ovary. A mean value of 19 500 eggs was calculated with a range from 5 700 to 41 800 eggs for females ranging in length between 22 cm –50 cm (TL). The number of eggs in the ovaries exponentially increased with the size of the fish (Saayman, 1986).

Largescale yellowfish migrate upstream to spawn after the first good spring rains and it can therefore be concluded that rainfall triggers spawning in this type of yellowfish. The rainfall probably alters the pH of the water that acts as a stimulant for the hypophysis to produce gonadotrophins for the development and release of eggs from the ovary and sperm from the testis. The preferred spawning areas are gravel beds in smaller tributaries of rivers. Preference is given to

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faster flowing water, with well-aerated spawning beds and a good food supply to sustain the fry after hatching (Vlok, 1997).

The frequency of spawning for Labeobarbus marequensis within a breeding season is twice as concluded in results obtained by Hecth (1986). Three different groups of ova were found during the breeding season in the ovaries of this species. The third group (6%) of eggs probably formed the recruitment stock for the following years breeding season. From these results it would also appear that the greater proportion of eggs are spawned during the first spawning run.

Artificial spawning Two attempts were made to artificially induce Labeobarbus marequensis to spawn in October 1980 at the Nwanedsi/Luphephe dams. Yellowfish were caught with nets and transferred to porta-pool

holding tanks with a continued water exchanges at a rate of 300 l per hour. Hormonal treatment was administered by injecting the fish intramuscularly behind the dorsal fin. Care was taken in all instances not to exceed a dose of 1 ½ ml. No information is supplied regarding types of hormones used or protocols applied. From the hormonal injection programmes administered it was not possible to strip a single female from any one of the four attempted trials. The conclusions made by Hecht (1986) in terms of the hormonal treatment, is that due to the extended breeding season and the different ova groups found, it is impossible to capture females that are all in the same stage of ovarian development (Hecht, 1986).

On two occasions ripe and running males and females were collected in the dam. The eggs were immediately stripped into a clean bowl and were fertilized by adding milt from a ripe running male. The fertilization process is not discussed in detail, but presumably the same protocols were followed as recently described by the same author on Clarias gariepinus. The eggs were fertilized for 6 minutes, and it was found that the sperm had coagulated and was removed with difficulty by washing the eggs in 0.9% saline solution for 10 minutes. By this time the eggs had swollen to approximately 2 – 3 times their normal size to ± 3.6 – 4.8 mm in diameter. Hatching was done in züger glasses with a flow rate of 1.3 ℓ/m. The eggs in the funnel started hatching after 86 hours (no temperature given) and the larvae were between 5.6 – 7 mm in length. Two days after hatching the yolk sac was reabsorbed and feeding trials were started. One group of larvae was given

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plankton, consisting primarily of Daphnia pulex, the second group were given a dry feed which consisted of equal parts torula yeast (Candida utilis) and fish meal. After 10 days, larvae in both groups attained a length of 12 – 15 mm. The author concludes that Labeobarbus marequensis larvae can be reared equally well on dry feed as on plankton for an initial period of 10 days (Hecht, 1986).

Hecht (1986) further concludes that the development of Labeobarbus marequensis from the fertilized egg stage up to the time the larvae hatch and the time intervals between the various developmental stages follows closely the time intervals between the various stages as found for Cyprinus carpio.

2.2.4. Labeobarbus Kimberleyensis Description The dorsal fin is D IV, 8-9 and the anal fin is A III 5. The primary dorsal fin ray originates above the pelvic, is an unbranched ray that is bony and spinous. The anterior rays of the anal fin are relatively longer than the other rays. The scales in the lateral line are between 37 – 45 (usually 42) , with 16 around the caudal peduncle. The mouth of this species is large and terminal with thin lips and two pairs of slender barbles. The eyes are dorso-lateral, thus not visible from below. The juveniles are silvery in colour, while adults are olive grey or light olive yellow (Skelton, 2001).

Distribution This species is endemic to the Vaal-Orange system, but only found in the larger tributaries and dams. Comprehensive population surveys in the Vaal River (Groenewald, 1957; Mulder, 1971 and Koch, 1979) showed that Labeobarbus kimberleyensis increased from 1.3 % in 1956 to 4.5% in 1969. However, since then (1969 to 1978) Labeobarbus kimberleyensis decreased to 3.3% of the fish community.

Habitat & Ecology Labeobarbus kimberleyensis is a predator favouring small fish, crabs and invertebrates. Gut length of this fish is indicative of its feeding behaviour. An average value of 114% is calculated for

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Labeobarbus kimberleyensis and this correlates to other species with similar feeding habits such as Labeobarbus mattozi and Clarias gariepinus (Mulder 1971).

Breeding behaviour Results obtained by Mulder (1971) indicate that males attain sexual maturity at a minimum length of 35cm, whilst females only reaches sexual maturity at 46cm, seven to eight years old. Sexual maturity was not related to length, but rather to age. No assumptions could be made in terms of increased egg production with increase in size. A female of 52.7 cm produced 41 000 eggs as opposed to another female of 54.4 cm which only had 16 000 eggs. Labeobarbus kimberleyensis is therefore a late spawner (older than 7 years) with low fecundity.

Artificial spawning As mentioned previously, anglers complained since 1956 that the largemouth yellowfish, Labeobarbus kimberleyensis, is rapidly declining from the Vaal River, and that populations of Cyprinus carpio, Labeo capensis and Labeo umbratus is rapidly increasing (Groenewald, 1957). Consequently Koch (1979) undertook a project on Labeobarbus kimberleyensis to: • Check on the distribution and densities of Labeobarbus kimberleyensis in the Vaal River system and compare these results with results of surveys done by Groenewald (1957). • Investigate the ecology of this species with reference to breeding and breeding season. • Propagate Labeobarbus kimberleyensis for distribution and restocking.

During September to December 1977 and 1978, brood stock was collected from the Vaalriver system and transported to the fisheries station at Lydenburg for artificial propagation trials (Koch, 1979). In order to get fish in top breeding condition, they were fed on a daily base with mince, liver and meat. When fish were ready for breeding (ripe running males were used as an indicator) an induction program was started on the females, which consisted of carp pituitary extracts (mass to mass) and pregnyl or estrumate. All breeding females (n=4) had an initial primer dose of one pituitary gland, 1ml estrumate (1000 iu/kg pregnyl) 24 hours before the main induction program was commenced (Koch, 1979).

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Females of 46cm (TL) and larger were selected for the trials as Mulder (1971) determined Labeobarbus kimberleyensis females to be only sexually mature at 45 cm (TL). This induced spawning program was unsuccessful and the authors suspected that the fish was not ready and the program to short to allow eggs to mature and become ready for spawning (Koch, 1979).

Interesting enough the fish that were returned to the dams did spawn naturally a month later. For the period 20 December to 20 January when spawning occurred, the water temperature ranged between 17 °C in the morning and 22 °C in the afternoon. As temperatures in the breeding dams were one degree higher, it can be concluded that Labeobarbus kimberleyensis started breeding actively at temperatures between 21 °C – 23 °C.

Of the juveniles observed, it was clear that there appeared to be three different age classes and shoaling was observed between aquatic macrophytes in the top level of the dam where no water movement (current) was present. Also, no juveniles were observed at the inlet where there was water movement or turbulence. Juveniles are slow growers and only attain a length of 100 mm (FL) after two years and 300 mm (FL) after five years (Skelton,2001).

Also in the then Cape Province the director of Nature and Environmental Conservation initiated a captive breeding program on selected threatened species at the Amalinda Fish Hatchery in East- London. The research was not only aimed at the propagation and restocking of threatened fish, but also research of their breeding requirements and behaviour. Induced breeding research was conducted on two large indigenous Barbus species, large mouth yellowfish (Labeobarbus kimberleyensis) and Cape white fish (Barbus andrewi). Initial attempts to spawn Labeobarbus kimberleyensis at Amalinda using standard hormonal (pituitary gland) injection procedures, were unsuccessful. During the spawning seasons from 1986 to 1989, captive spawning studies was done on Labeobarbus kimberleyensis using a combination of environmental and hormonal stimulation. The brood stock was held in fertilized earth ponds (0.2 – 0.6 ha) at low stocking densities of less than a hundred per hectare. Fish acid oil enriched trout pellets were fed at about 2% of the total body mass of the fish, 5 times per week. This was done, as ample food supply is an important factor for gonodal development. Spawning ponds were constructed consisting of a 0.5 ha earthen pond with an artificial gravel bed (U-shaped and 12 m2, with a top layer of rounded river

Chapter 2 Literature Review page 2-14 Reproduction Strategy Of Labeobarbus Polylepis (Smallscale yellowfish) gravel 20 – 50 mm in diameter) situated at the inflow channel. Prior to breeding trials, these ponds were allowed to dry out thoroughly and stand empty for at least a month before use. During the months October to December brood stock were netted from the holding ponds and stocked into the half filled spawning ponds that were in the process of filling. The water levels were manipulated so as to ensure that the gravel spawning bed was inundated about 24 – 72 hours after the fish was stocked. A water flow of approximately 500 ℓ/min was maintained over the gravel beds during spawning trials. When the fish were observed on the spawning bed, and displayed typical spawning behaviour, they were netted and taken to the hatchery where the hormone injection procedures were applied. In an attempt to standardize pituitary dosages, glands from sexually ripe 1kg common carp (CPG) were used. A standard hormone injection procedure were a series of two injections given 14 to 16 hours apart, the first consisting of 0.5 – 1.0 CPG and the second 1.0 – 2.0 CPG /kg of recipient. The second injections were given late at night in anticipation of ovulation 6 – 12 hours later. Both species, Labeobarbus kimberleyensis and Barbus andrewi, spawned in the ponds within 12 – 24 hours after the gravel bed was covered with an adequate depth of water. Interesting is to note that there were total or very high mortalities of eggs and free embryos, probably due to low oxygen levels in the gravel. Bok (1990) suggests that the combination of stimulatory cues provided in the spawning ponds, namely the simulation of flooding and the presence of suitable spawning substrate near the inflow, stimulated the final gonodal maturation, ovulation and even ovi-position in both species. He further speculated that the influence of substances such as petrichlor (organic compound) released from newly inundated earth may also play a role.

2.2.5. Labeobarbus Capensis Description The dorsal fin is D IV +9 and the anal fin is A III +5. The primary dorsal fin ray is flexible and segmented and originates above or slightly in front of the origin of the pelvic. The scales are in a lateral line 40 – 45, with 16-20 around the caudal peduncle. The mouth has variable lips with two pairs of barbles (Cambray, 1999).

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Distribution This species is endemic to sections of the Olifants River section in the Western Cape. The abundance of this species is low with dwindling numbers due to the introduction of alien predators, poor land management and the construction of main channel dams restricting migrations.

Habitat & Ecology Adults are pool dwellers, most often found in clear, rocky pools, or deeper reaches, also often associated with strong flow. The eggs and free embryo’s are riffle dwellers and early juveniles are edge dwellers with older juveniles inhabiting pools, sheltered backwaters and marginal areas of the main stream. They can also be active in the main channels of tributaries where they maintain position in the gentle summer flows (Skelton, 1987). This yellowfish is an omnivore with a diet of algae, aquatic invertebrates and larger fish eat small fish, frogs and crabs.

Breeding behaviour Labeobarbus capensis is a multiple spawning species and each spawning period lasts a day or two. According to Cambray et.al.(1997) this species can be classified as a repeat spawner. The females are larger in size than the males, and are powerful swimmers maintaining their position over the mid-channel cobble/gravel spawning beds for hours. The males on the other hand position themselves in cover, occasionally darting out to align with the females to spawn. The spawning activity is described by Cambray et.al.(1997) as large individuals maintaining position on the spawning bed, which is then joined by smaller fishes darting out of the vegetation cover. Single, but up to three fish were observed to quickly line up facing upstream, and close together. Rapid vibrations of the fish for 2 –10 seconds released a cloud of milt across the bed, and on no occasion did any of the fish break the surface of the water. After the spawning act, the smaller fish moved away, usually upstream or to the edge cover, while the larger fish either moved upstream, fell away in a tumbling manner downstream, or maintained position on the spawning bed. This behaviour was interpreted by the author as a possible suggestion of being a repeat spawner (Cambray et.al., 1997). According to Cambray (1991), the reproductive style of Labeobarbus capensis belongs in the: ethological section of nonguarders (A.); the ecological group of open substratum spawners (A.1.); and the guild lithophils (A.1.3.) which are rock and gravel spawners with benthic free embryos (Balon, 1975). Labeobarbus capensis eggs are non-adhesive and the hatched free

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embryos are photophobic and hide between and under cobbles. Additional reproductive traits of this species include relative late maturity and increasing reproductive effort with age.

Labeobarbus capensis is a non-guarding, open substrate spawner that produces non-adhesive eggs. On the spawning beds below the Clanwilliam dam, eggs were found in a shallow, minor channel characterised by a lack of instream or overhead vegetation cover, and on a substratum of 50% small boulders, 30 % small cobble and 20 % large gravel. The eggs and free embryos were lodged under large boulders, between the cobbles and gravel, and in a current velocity of 2 m/sec, in a water depth of 22 cm. The free embryos are photophobic and remain in the same habitat as the eggs for 10 – 12 days (at 22 ˚C) and then during the swim-up stage, the free embryos are carried downstream to shallow, placid, sandy areas where they commence feeding as larvae (Cambray, 1999). Breeding occurs from spring to high summer during flood freshets suggesting that a strategy of smaller but more frequent water releases from dams would be of greater benefit to sustaining the species (Cambray et.al., 1997).

Labeobarbus capensis is a large fish species, attaining a length of almost 1 m and taking 5 – 7 years to mature. Historically before the two major dams in the Olifants River were built, Labeobarbus capensis congregated below natural rapids, and then undertook mass upstream migrations during the period September to December, in search of suitable spawning beds of clean gravel in the shallow portions of the river. The fish used to congregate in large numbers on the spawning beds, and the eggs and milt appeared to be released indiscriminately. After spawning the adults would drift back to the deeper waters (Hey, 1947 and Impson, 2005). Gonad development increased in August and September, but peaked in October to December, and starts to decline from January. The adults are most often found in clear, rocky pools, or deeper habitats often associated with strong flow, whereas juveniles mostly inhabit pools, sheltered backwaters and shallow marginal areas of the mainstream (Cambray et.al., 1997).

King et.al. (1999) investigated the linked effects of dam released floods and water temperature on spawning of the Clanwilliam yellowfish in the Olifants River below the Clanwilliam Dam. Of special interest in this winter rainfall region, was small pulses (freshets) of higher flow that occurred in the dry season (November to April). Research was done on the link between these freshets and

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spawning behaviour of this species. Hypolimnetic and epilimnetic releases were artificially manipulated according to the size that was earlier found by Cambray et al.(1997) to induce spawning. However, during this study (King et.al., 1999) a hypoliminetic fresh of the same size, duration and timing as those linked with spawning success, failed to induce spawning. The differences in the thermal regime of water releases appear to be responsible (King et.al., 1999). Warm (19 ºC – 21 ºC) epiliminetic freshets (15 hour duration) correlated with fish moving onto spawning beds and exhibiting pre-spawning behaviour. However, the fish moves down stream away from spawning areas when cold (16 ºC – 18 ºC) hypoliminetic base flows were released. Also the presence of dead and deformed larvae suggests that cold water may have had a detrimental effect on the development of embryo’s and larvae. These freshest at appropriate time of water temperature (above 19 ºC), stable and rising, should increase spawning success of Labeobarbus capensis in the Olifants River. Nevertheless, successful spawning will not lead to high recruitment if the water temperature is not maintained at appropriate levels for the development of embryo’s and larvae (King et.al., 1999).

In Labeobarbus capensis, rising water temperature appear to be the link which bring fish into breeding condition. Once in breeding condition, fluctuating releases of water appear to trigger spawning.

Artificial spawning Attempts to initiate spawning of Labeobarbus capensis at the Clanwilliam Fish station by holding fish under simulated “ natural” conditions in earth ponds, with running water and gravel spawning beds were unsuccessful. Furthermore, initial attempts to induce this difficult fish to spawn using standard hormone induction techniques with pituitary gland homogenate (PGH) injections, were unsuccessful. However, in 1990 trails that were conducted using Lutenising hormone releasing hormone analogues (LHRHa) have had some success, although limited and inconsistent. Aquaspawn, a synthetic Gonadotropin releasing hormone (GnRH) analogue and Domperidone was tested by Cape Nature Conservation fishery staff on this species from October to December 1991. Three female fish received a pellet implant of aquaspawn, plus additional injections of Aquaspawn and Carp Pituitary hormone (CPH). Two of these fish produced viable eggs, both with a good hatching rate of over 70% ( Bok, 1992).

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Under hatchery conditions Labeobarbus capensis eggs were negatively buoyant and slightly adhesive, until water hardened after approximately 45 minutes. From captive breeding experiments, the water-hardened eggs were recorded with diameters of 2.60 mm – 2.67 mm, with a yolk diameter of 1.98 mm. Eggs kept at 22 ºC – 23 ºC took 63 hours before free embryos hatched. These were 7.38 mm (TL) and photophobic, and after 10 – 12 days the larval fish began to feed. It was therefore calculated that at water temperatures between 22 ºC and 23 ºC the embryos spend 9 – 10 days on the spawning beds before the swim-up occurred. They will then be carried downstream by currents to shallow and quieter water where they would commence feeding and develop into larval fish (Cambray, 1991 and Bok, 1992).

2.2.6. Labeobarbus Polylepis Description The dorsal fin is D IV, 8 and the anal fin is A III +5. The primary dorsal fin ray is flexible and segmented and originates above or slightly in front of the origin of the pelvic. The scales are in a lateral line 36 – 44 (usually 40), with 14 – 18 (usually 16) around the caudal peduncle. The mouth is sub terminal and has variable lips with two pairs of barbles. Males and females develop small white tubercles on head, upper body scales, anal and dorsal fin rays. The juveniles are silvery with dark spots on the body, while adults are dark olive green above and bronze on the sides. The fins are characterised as dark gray and –green (Skelton, 2001).

Distribution Labeobarbus polylepis is a coldwater species that is not found at altitudes below 600m, and occurs in the southern tributaries of the Limpopo system, as well as in the Incomati and Pongola river systems (Skelton, 2001).

Habitat & Ecology This species is known to prefer deep pools and flowing water of perennial rivers and readily occurs in dams (Skelton, 2001). Results by Austin et.al. (2005) have indicated significant morphological differences between two Labeobarbus polylepis populations; also Gaigher (1969) found morphological variations in the Labeobarbus polylepis populations in Mpumalanga.

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Within Mpumalanga the importance of Labeobarbus polylepis is significant and this species is considered as one of the more important species that provide aquatic ecosystem information that is used to establish the management scenarios of aquatic resources. Many Labeobarbus polylepis populations within these rivers have historically been isolated due to natural geological formations such as waterfalls acting as boundaries for populations and recently dams (e.g. Nooitgedacht, Vygeboom and Blyderivierspoort dams) has isolated populations (Mulder et.al., 1997).

This species feeds mainly on algae in winter months, as well as on aquatic insects in the summer months, but also takes mussels, snails, crabs and small fish. They reach a maximum size of 58.5 cm (TL) and a weight of 6.8 kg. Breeding occurs during spring and summer. Males mature at a smaller size (17 cm FL), and females at 30 cm (FL) (Skelton, 2001).

Goldner (1969) suggest Labeobarbus polylepis to be a facultative feeder (omnivore), utilizing a wide variety of food. During autumn/winter filamentous algae are utilised and the rest of the year bentic invertebrates are the predominant food.

Breeding behaviour Meyer (1972) reported upstream migrations of Labeobarbus polylepis during spring and early summer. Batchelor (1974) found similar results during a mark and recapture study in the Doorndraai Dam, when marked Labeobarbus polylepis were recaptured in the early spring at the river inlet of this dam. He further speculates that rain and the associated petrichlor urges these fish to migrate upstream and that the gravel bottom where the water is fast flowing, could be the spawning beds. The sex ratio in Doorndraai Dam between males and females were determined at 44.4% males and 55.6% females. However, Gaigher (1969) found this sex ratio’s to be 60.2 % males and 39.8% females. He also found that males become sexually mature in their third year at 17 cm (FL) while females only reach sexual maturity at 28 cm (FL) at 4 years.

Artificial spawning Throughout the Literature review nothing was found regarding the artificial propagation of Labeobarbus polylepis, confirming and indicating the lack of research done in this area.

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Skelton (2003) states that there is still much to learn about these fascinating fishes, in particularly we need to know more about their phylogenetic relationships, their osteology, genetics, biology and ecology. We also need to understand their biogeography, and we need to ensure that the rivers and ecosystems where they live are conserved.

2.3. CONSERVATION

The need to conserve the freshwater fishes of Southern Africa has increased in the past two decades in accordance with the global concern with the state of the environment. The attitude of the established conservation authorities in the 1960 to 1970’s were still dominated by fishery policies supporting the active production of alien sport fishes. The complete change of this prevailing paradigm was necessary and the historical case study of the Clanwilliam yellowfish, Labeobarbus capensis, illustrates this well.

This yellowfish was one of the first freshwater fish to be noted by western settlers on their arrival in the Cape in the 17th century. Although the Clanwilliam yellowfish enjoyed an outstanding reputation as angling species, it was considered necessary to enhance the angling qualities of the Olifants River system by introducing (1930-1940’s) three different species of black bass (Bruton & Marron 1985; De Moor & Bruton, 1988). After public complaints on the deterioration of yellowfish angling in the 1960’s, surveys were conducted that led to the Cape Nature Conservation expressing their concern about this species. The introduction of bass species and the construction of two large mainstream impoundments (Bulhoek, 1922 and Clanwilliam Dam, 1935) led to the decline of this species. The Clanwilliam yellowfish was listed as rare in 1977 and 1978 red data book and as vulnerable in the 1996 IUCN redlist (Skelton, 2000). Since the 1960’s the conservation authorities has given Labeobarbus capensis considerable attention and a hatchery was constructed on the riverbanks of the Olifants River for breeding and restocking purposes (Scott, 1982). However, due to the lack of strategic planning and limited financial support, little cultured stock was produced.

In South Africa, as elsewhere, the rapid deterioration in the status of indigenous freshwater fishes has been prominent in the last 50 years. The awareness of the decline of indigenous fauna species

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became evident with the establishment of the nature conservation departments in the 1950’ s and 1960’s. In all the provinces surveys were conducted to determine the status of indigenous fish populations and to establish the impact of alien species in the natural systems. In the former Transvaal and Cape Province the surveys clearly indicated the negative impact of alien species on indigenous fishes. The authorities responded accordingly with changes in policy towards the breeding and stocking of sport fishes (alien) and with research programmes into indigenous fish species and their conservation (Skelton, 1987; Cambray et.al. 1997 and Skelton, 2000).

Skelton (2000) states that the southern fish fauna is relatively depauperated (33 species in 4 families) with characteristically narrow distribution ranges, and are often endemic to a single or few drainage basins. The taxa here evolved in isolation with the lineages fragmented, linked or removed by changes in drainage systems over time. These taxa generally display low resilience to the environmental disturbances induced by man and a high proportion (60%) is listed as threatened to a greater or lesser extent. The impact of introduced alien fishes has been particularly severe on these southern elements, as a result of this low resilience. These alien predators have reduced some temperate indigenous fish species populations to pockets of isolated fragments.

From the late fifties to the early seventies an increased interest developed by the then Four Conservation Authorities into the feasibility of propagating indigenous yellowfish species to meet the ever-increasing demand for sport angling. In the Transvaal, work on the large yellowfish species was conducted by Groenewald (1957 & 1961) who taxonomically tried to distinguish between the different yellowfish species, and produced an information leaflet “ An angler’s guide to the yellowfishes of the Transvaal.” This booklet is an indication of the then growing interest of anglers in the yellowfishes for its angling potential at the time. Surveys were conducted by Groenewald (1957) to determine distribution localities of Labeobarbus kimberleyensis and Labeobarbus holubi in the Vaal River.

In the Orange Free State (Nature Conservation Branch) research was done on the yellowfish species, Labeobarbus kimberleyensis and Labeobarbus aeneus, but very little published information exist on activities in the Free State. Already in the sixties, a concern arose regarding the rapid declining of Labeobarbus kimberleyensis and Labeobarbus holubi in the Vaal/Orange

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River system. Mulder (1971) did an ecological study on the angling fishes of the Vaal River system with special emphasis on Labeobarbus kimberleyensis. This study concentrated on the geographical distribution, length-weight relationships, growth rate, feeding habitats and reproduction of mainly Labeobarbus kimberleyensis and to a limited extent on Labeobarbus aeneus. Furthermore, various attempts were made on the propagation of Labeobarbus kimberleyensis and Labeobarbus aeneus. Le Roux (1968) states the importance of this as follows: “After the establishment of the Nature Conservation Branch, one of the first objectives was to propagate these species artificially, so that young fish would be available for distribution in waters from which it was absent, or for re-stocking waters where the natural populations had been reduced for some or other reason.”

Furthermore, in the Free State, according to Fouche (2006), population studies were done in 1989 of all the large dams and rivers in the Orange Free State. Labeobarbus aeneus was found to be very abundant in the Sterkfontein Dam. In the Gariep Dam, the condition factor of the Labeobarbus kimberleyensis population was found to be the lowest of all surveyed sites. He related this to the turbidity and that Labeobarbus kimberleyensis is a predator and need visibility to hunt. In 1988 Labeobarbus kimberleyensis brood stock collected from Wuras Dam was artificially bred using an induction program of synthetic hormones. This program appeared to be successful as 2000 Labeobarbus kimberleyensis juveniles ranging between 50 – 20 cm (TL) were translocated to Sterkfontein Dam in April 1989 (Fouche, 2006).

The ecosystem based and biodiversity (populations and communities) philosophies that embrace the River Continuum Concept, as well as the need to determine “in-stream flow requirements”, became prominent during the 1980’s. This included studies to determine strategies for water releases from the mainstream dams on the system. The effect of experimental flood releases on the breeding of the Clanwilliam yellowfish has provided valuable information for the conservation of this species (Cambray et.al. 1997).

The form, hydrology and functioning of rivers worldwide have been increasingly modified by a range of human activities, and these geomorphic and hydrologic changes influence the structure and dynamics of biological communities in the river (Welcomme et.al., 2006). This author

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emphasizes the significance of changes in the timing, duration, amplitude and other characteristics of flood regimes on various fish species. As there is also a vast literature on the responses of some fish species to changes in the morphology of rivers, the availability of habitats and the connectivity between them, it is nevertheless impossible to assess the impact of changes in hydrology or morphology on most species.

Dams commonly alter the natural flow patterns below dam walls and there is usually a reduction in the incidence and extent of floods. River regulation normally impose more stable conditions, which can be more favourable to introduced fish such as carp, Cyprinus carpio, and is disadvantageous for the native ichthyofauna. As more rivers are modified by man, river managers require information on what allowances should be made for the maintenance of the downstream aquatic environment. There is thus a need in South Africa to develop suitability index graphs for each of the major life stages of some of the fish species. The consequences of river regulation are mainly detrimental for the lotic biodiversity (Hellawell, 1988). As in other countries fish species and their habitat are threatened by river regulation, since there are ever increasing barriers to the movement of migrating fish species caused by dams, weirs, causeways and culverts. These barriers to fish movement cause a loss of spawning grounds and fragmentation of the populations, resulting in a loss of continuity and preventing re-colonisation of the area following severe draught periods (Cambray, 1991). Furthermore, downstream refuge seeking movements are limited because of predation by introduced species (such as large mouth bass, Micropterus salmoides) in these artificially lentic created habitats.

Poor farming practices have changed many streams from narrow, clear water with deep holes to wide, shallow muddy tracts. During periods of high flow this results in high turbidity, consequently silt filling holes between boulders preventing the possible interstitial travel of fish between disconnected pools, as well as destroying the spawning habitat for the species with demersal, non- adhesive eggs. The infilling of interstices can also reduce the amount of cover available for the larvae and juveniles of some species. Previously flush flooding would have scoured some of the river reaches, but with the building of dam walls, the extent of scouring has been reduced and silt deposits may accumulate that could asphyxiate the eggs and early free embryo’s. Flood velocity

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flows are necessary in many rivers to clean the substrate and maintain the physical integrity of the river channel (Cambray, 1991).

In South Africa basic knowledge of species biology and ecology is simply too limited at present to provide effective management advice. There is a strong need for further detailed studies on the ecology of keystone species in the various systems in South Africa. Sound basic knowledge is irreplaceable when it comes to making decisions on the environment (Skelton, 2000). Long-term conservation will depend on effective ecosystem management practices and the role of flagship species to create public awareness of the need for conservation of freshwater systems, is one of the most important steps made in the development of modern conservation ethics.

The new National Water Act (NWA, 1998) has foreseen the importance to manage aquatic systems on a catchment scale. This Act has thus implemented procedures (RDM and reserves) to assess, establish and manage the use of aquatic resources based on specific regulation-based scenarios of the catchment systems.

The new National Environmental Act: Biodiversity Act gives national importance to the management of species in aquatic ecosystems. The Act also facilitates the listing and development of conservation protocols for unique (endangered) indigenous species and ecologically important and sensitive ecosystems that require protection. The associated protocols for these listings are, however, dependant on detailed knowledge of the species, their biology and ecology. Also, sensitive species (or flagship species) can be used as indicator species to assess the functionality of the ecosystem.

FOSAF (Federation of South African Flyfisherman) started with a program promoting yellowfish for its angling and fly fishing potential and accordingly a yellowfish workgroup was established that promotes and coordinates research and development activities of the yellowfish species in South Africa (Bainbridge, 1997). Mpumalanga Parks Board embarked on a program to look at the ecology, breeding behaviour and propagation of Labeobarbus polylepis (Engelbrecht, 1997 and Roux, 1997).

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In a recent study (Mulder et.al., 1997) significant differences were found between four populations of Labeobarbus polylepis tested from the three river systems where this species occurs. At present, recommendations are that fingerlings only be stocked within catchments, and that restocking only be allowed in dams until a more in-depth study is completed.

It is accepted that indigenous species released into stretches of river, which they previously occupied, would have a smaller ecological impact on aquatic ecosystems compared to exotic species (Impson & Bok, 1995). However, Cambray (1998) cautioned against the introduction of such large predators as yellowfish into rivers that did not form part of the natural distribution of this species. According to Mulder (2000), in a species such as Labeobarbus polylepis which is distributed over different river systems, a lack of migratory path ways and isolation between the systems may lead to a high degree of genetic divergence among subpopulations. This can produce a high fragmented gene pool where opportunities for population differentiation, some of which may be adaptive, are enhanced. Mulder (2000) states two options with breeding and release programs: • Supportive breeding is when a fraction of the wild parental population is brought into a hatchery for artificial reproduction. The offspring are then released into the natural habitat to breed with the wild population. This is characterised by the fact that no exogenous genes are introduced into the wild population, but this may lead to a reduction in the diversity of the wild population (Mulder, 2000). • The alternative is to maintain one brood stock with the release of fingerlings throughout the distribution range. Care should be taken when selecting the brood stock, as “ all” genetic characteristics should be represented in the brood stock, so that natural selection can take place wherever fingerlings are released. However, populations may be genetically different following isolation or responses to changing environmental conditions (Mulder, 2000).

It seems that both methods may have negative effects on the wild populations. The appropriate target from a conservation point of view should be sufficient genetic variability in order to permit the population to maintain the potential to respond to environmental perturbations (Mulder, 2000). Co- operation with Nature Conservation Authorities is necessary to improve management plans and strategies, and to deal pro-actively with genetic management of natural populations and the release of hatchery bred fingerlings into wild populations.

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Relatively little is known about the ecology, which includes habitat preferences, niche differentiation, breeding ecology and early life history patterns of most indigenous fish species of South Africa. This specific information is of utmost importance for management implication. Literature surveys reveal this lack of knowledge also apply to the South African Cyprinids, and to Labeobarbus polylepis in particularly.

Vlok (2000) presented a paper at the Yellowfish Symposium (Yellowfish Working Group Conference) held at Muden KZN on current and past research being done on yellowfish. The title of this paper being: Yellowfish research, a dark picture. In this paper, results from a literature search (1998) done on the water research commission database, JLB Smith Institute and Albany Museum, was discussed. The results being only 88 hits on yellowfish in the southern African region. This included all types of references, the scientific references was 65 in total. All references in scientific articles do not necessarily mean that the work reported on were on yellowfish. Some of these articles are about exotic species or parasites and yellowfish are mentioned in the key word list. An analysis of the references indicate that most of the work had been done on Labeobarbus aeneus (42 scientific publications) followed by Labeobarbus kimberleyensis (18 scientific publications) and Labeobarbus marequensis (13 scientific publications). The remainder of the species has less than 10 references with Labeobarbus polylepis only 4 scientific publications (Vlok, 2000).

2.4. ENVIRONMENTAL PARAMETERS / CUES TO STIMULATE SPAWNING

It is known that fishes integrate their physiological functions with environmental cycles and that the endogenous stage of physiological process is responsible in part for seasonal reproduction. In addition certain proximate environmental factors that act as cues for the approaching favourable season for reproduction impinge on the exteroceptors and, through them, affect the central nervous system, the pituitary and finally the gonads. It is through such environmental factors that the endogenous rhythm is brought into phase for the precise breeding time (Crim et.al., 1983).

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The implication of successful spawning for the survival of fish populations is of great importance: no spawning is equivalent to no recruitment and will lead to population decline. Each species has a different breeding strategy and many species such as eels have complex life cycles. Furthermore, different fish species reach sexual maturity at different ages, spawn in different seasons and have different environmental requirements. Many of the requirements have some seasonal factor that induces spawning. It is usually difficult to determine the exact factor and may in fact relate to a combination to environmental conditions. A pre-spawning migration is essential for many species. An environmental cue such as rising water levels often initiate such migrations, which is required for successful spawning.

Spawning seasons are generally the same from year to year, although exact spawning times may differ slightly due to variation in environmental conditions. The spawning season reflects the environmental conditions required to maximize spawning success for the given species. In many inland species, fish spawn during spring and summer when day length and temperatures are increasing. These conditions allow eggs and juveniles to maximize growth rates through increased metabolism and to utilize increased food supplies associated with increased energy input. In contrast coastal species which have larvae swept to sea, spawn during autumn and winter which allow juveniles to re-enter fresh water during spring and summer. The spawning behaviour of fish during spawning is generally determined by their reproductive strategy (Balon, 1975).

A complex interplay of environmental factors appears to be involved in fish migration in rivers: • the photoperiod – in many salmonids that spawn in autumn, the gradually increasing photoperiod followed by decreasing ones, or even short photoperiods, play a dominant role in the regulation of reproductive cycles. • temperature (atmospheric and water) – in cyprinids and perciform fishes, temperature may also be a significant regulatory factor in the reproductive cycle. • weather cycles – atmospheric pressure and rainfall • water quality – dissolved oxygen, pH, hardness, salinity and alkalinity • rainfall – in the Indian sub-continent a vast majority of the freshwater fish species breed during the monsoon season when the rainfall is the heaviest.

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• flooding and water current – fresh water fishes of the Murray-Darling River system in New South Wales, Australia, are stimulated to spawn when flood waters come into contact with dry soil, and the association with petrichlor (Humphries et.al.,1999). • tides and cycles of the moon • spawning substrates – aquatic plants, gravel, sticks, spawning caverns • disease and parasites • presence of other fish – i.e. shoaling • nutrition and food availability

Numerous studies states increased flow (discharge) and temperature as a cue to initiate spawning migrations (Welcomme, 1985 and King et.al., 1999). Studies suggested that increasing and decreasing photoperiod was the predictive, proximate factor in temperate areas, enabling fish to sense the spawning season (Jonsson, 1991). He also states that in most parts of the world there is an obvious link between photoperiod, temperature and river flow, and the viability of the latter two accounting for the annual variation in spawning migrations.

Temperature and daylight length (usually correlated and difficult to distinguish as cues) are thought to be important in initial spawning. A temperature regime of five days of increasing temperature within a certain range may be more important than a specific temperature. The conditions that induce spawning have usually been inferred from available data rather than proven conclusively.

Suitable spawning sites need to be available in order to maximize the survival and development of eggs and fry. Different species require different spawning sites and such sites provide protection from physical damage and predation. Depositing eggs in less suitable areas such as sediment- covered substrate will lead to reduced egg and larval survival. An assurance of both appropriate condition and the protection of spawning sites are vital for successful spawning. Because the precise site of egg laying is often not known, the spawning site is recorded as that where eggs were located.

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Other physical chemical requirements may be necessary for spawning and includes pH, water hardness, salinity gradient, and the concentration of minerals or other chemicals.

For riverine fish the final phase of gonad maturation and the release of gametes at a specific spawning site, may require one or all of the following stimuli: increased current speed, water quality changes, barometric changes, or feromone releases (Nesler et.al., 1988). Fish in the South Central African freshwaters are governed by biological rhythms, which is associated with the marked seasonal summer annual rainfall during which time breeding takes place (Jackson, 1989). Most of these fish breed during the summer months and have a short annual spawning period, often preceded by an upstream migration out of the main waters, and eggs are shed among temporary inundated vegetation in river floodplains and oxbows. This usually takes place early in each rainy season, usually around late November, when the first floods have swollen the rivers and penetrated the lakes. The eggs and young are thus placed in a refuge, safe from predators and these contain ample microscopic food. Here they grow rapidly until the dry season forces them back into the main water body to complete the annual cycle (Jackson, 1989).

The reproductive and recruitment characteristics of moggel (Labeo umbratus) populations were examined in four small South African reservoirs. Their reproduction is characterised by an extended spawning season, high fecundity with a short incubation period and a rapid larval development. This strategy appears ideally suited to the highly variable environment of small reservoirs. In the two reservoirs where samples were conducted monthly, the gonado-somatic index was positively correlated with both water temperature and daylight length, and the spawning success of moggel appeared to increase when there was early spring and consistent summer rainfall (Potts et.al., 2005).

The spawning of Barbus mattozi is highly seasonal and timed to take place with the first floods. In the Mtsheleli River (Zimbabwe) it was observed that the entire adult population of Barbus mattozi migrated upstream to spawn during a 24 hour period of heavy rains and flooding of the river (Donnely & Marshall, 2005).

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Barbus anoplus has been studied in detail by Cambray (1983) and Cambray & Bruton (1984, 1985) and they conclude that the reproductive strategy of this species evolved in a seasonally fluctuating riverine environment. Peak spawning usually occurs after a period of steady rainfall and a spawning migration is not necessary as the fish can spawn locally if there is a rise in water level and the marginal vegetation is flooded.

2.5. ARTIFICIAL PROPAGATION OF FISH SPECIES

Certain fish species do not reproduce spontaneously in captivity as many of them spawn in environments that are nearly impossible to simulate in a hatchery. Hormone induced spawning is the only reliable method to induce reproduction in these fishes.

In fish the reproductive process involves three basic steps: • Maturation - the development of the gametes (eggs and sperm) to a point where fertilization can occur. • Ovulation – the release of eggs from the ovary • Spawning – the deposition of eggs and sperm (Mittelmark & Kapuscinski, 2004)

Fish have evolved to reproduce under environmental conditions that are favourable to the survival of their young. Long before spawning, seasonal cues begin the process of maturation. When the gametes have matured, an environmental stimulus may signal the arrival of optimal conditions for the fry, triggering ovulation and spawning. Examples of such environmental stimuli are changes in • the photoperiod, • temperature (atmospheric and water) • weather cycles – atmospheric pressure and rainfall • water quality – dissolved oxygen, pH, hardness, salinity and alkalinity • flooding and water current • tides and cycles of the moon • spawning substrates – aquatic plants, gravel, sticks, spawning caverns • disease and parasites

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• presence of other fish – i.e. shoaling • nutrition and food availability. These factors do not function independently, but are interrelated.

A variety of sensory receptors detect these cues that include the eye, pineal gland (an organ in the dorsal part of the forebrain that is sensitive to light), olfactory organs and thermo-receptors. The hypothalamus is sensitive to signals from these receptors and release hormones in response to environmental cues. The most important of the hormones are the gonadotropin releasing hormones (GnRH) that travel from the hypothalamus to the pituitary gland. The pituitary gland is responsible for a variety of functions that include growth and reproduction. The pituitary in turn on receiving GnRH will release gonadotrophic hormones into the bloodstream. These released hormones travel to the gonads that synthesize steroids responsible for final maturation of the gametes. Some of the significant advancements in the field of aquaculture during recent decades are the refinement of techniques to induce reproduction in fish (Mittelmark & Kapuscinski, 2004).

There are two main strategies used to induce reproduction. The first is to provide and environment with cues similar to that in which spawning occurs naturally. For instance, the presence of vegetation and increase in temperature usually works for gold fish. Also in changing the photoperiod in a hatchery, the maturation and ovulation can be accelerated in many salmon and trout species. The second strategy is to inject the fish with one or more naturally occurring reproductive hormones or their synthetic analogues. This strategy is only effective in fish that are already in breeding condition, and have mature eggs in which the germinal vesicle has migrated. Two techniques are commonly used, sometimes in conjunction with one another. The first technique is used to manipulate maturation and the second to induce ovulation (Mittelmark & Kapuscinski, 2004).

The primary substances used for induced spawning have been: • Pituitary extracts • Purified gonadotropin (human chorionic gonadotropin – HCG) to stimulate the ovaries and testis • Lutenising hormone releasing hormone analogue (LHRHa) alone or

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• In combination with dopamine blockers which enhances the potency or LHRHa to stimulate the pituitary • Steroids to stimulate the gametes directly

The appropriate hormone preparation should be selected on the basis of the species to be spawned and the availability of the hormones (Rottmann et.al., 1991a).

External appearances of brood fish have long been used to assess the stage of sexual development. In some species males change in appearance during the spawning season, and these physical changes make it relatively easy to identify sexually mature males. Milt can usually be stripped from males of most species when they are ready for spawning. On the other hand, the characteristic plumpness of the abdomen and redness of the vent of females can be particularly subjective and confusing. Several tests are available to determine the developmental stage of the eggs in the female ovary. Two common methods are: the egg appearance and the physiological state of the egg, but both require that egg samples be taken from the fish. The diameter and appearance of the egg, as well as the position of the nucleus in the egg are visual indicators of development. An understanding of sperm viability and egg stage development will greatly improve the success of hormone induced spawning of fish (Rottmann et. al., 1991c).

The physical injury and physiological stress of capturing, handling, transporting, injecting and holding of brood fish can have a negative impact on the spawning success, more so than any other factor (Rottmann et.al., 1991e). The handling stress and physiological process of final maturation of eggs and sperm increase the oxygen demand of the brood fish. High temperatures normally accelerate egg maturation, resulting in greater oxygen demands by the fish. Female brood fish ready for spawning is in a delicate condition and should they be stressed or injured may undergo rapid physiological changes that can result in reabsorption (breakdown) of eggs in the ovary. The well-known causes of stress, such as crowding, dissolved oxygen depletion, rapid changes in temperature and osmotic imbalances must be avoided. Sub-optimum conditions, while not immediately lethal, may stress brood stock and result in delayed mortality or failure to spawn. Thus, reducing stress and injury to brood stock can greatly increase the success of hormone induced spawning (Rottmann et.al., 1991a;b).

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Intramuscular injections are commonly done on the dorsal part of the fish above the lateral line and below the anterior part of the dorsal fin. Two dosage levels are commonly used: a preparatory dose and the decisive, or final dose with a gap time of generally 12 – 24 hrs. The preparatory dose brings the fish to the brink of spawning, whilst the decisive dose induce ovulation. In general the preparatory dose is 10% of the total dose, but for some fish several preparatory doses may be necessary.

The time between the final or resolving dose of hormones and ovulation is referred to as the latency period. This is usually dependent on the species of fish, water temperature and hormone preparation used. The latency period is especially important when hand stripping is done. In general the eggs of tropical and subtropical species of fish become overripe more quickly than those that spawn at cooler water temperatures. According to Rottmann,et.al.(1991d) the maximum period between ovulation and deterioration of the egg quality for a range of carp species vary between 30 to 80 minutes. For most species, ovulation can best be verified by checking the female to determine when eggs flow freely from the vent. Tropical species are usually checked every 45 minutes until ovulation is verified, whilst temperate water species are usually checked every hour. When eggs flow freely from the vent, complete ovulation has occurred. The dry spawning technique is described in detail by various authors (Steyn et.al.,1996). And it is agreed by them that it is important to ensure that no water comes in contact with the eggs until after the milt is added and mixed. Water activates the sperm and also causes the opening through which the sperm enters the eggs (micropyle) to close. For many fish this closure takes place within only 45 to 60 seconds.

Ovulated eggs of many species, such as sturgeon, common carp and channel catfish, becomes sticky after contact with water. During natural spawning this stickiness causes the eggs to attach themselves to a substratum of rocks or aquatic plants. However, this stickiness causes problems during incubation in a hatchery scenario. Several common preparations such as urea and salt solution, tannic acid and sodium sulfite solutions can be used to eliminate the sticky layer of fish eggs.

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Stripping should be carried out as soon after ovulation as possible. Fish should be anesthetized and examined for readiness 6 – 12 hours after the final injection. Before stripping, both males and females should be cleaned and dried because residue anesthetic will kill sperm. A fish that does not have mature gametes will not produce viable eggs or sperm no matter how many times it is injected with hormones. Ripeness is the result of environmental factors working over a period of time leading to maturation of gonads and production of viable eggs.

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