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Chapter 2: Habitat and Population Selection

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Chapter 2: Habitat and Population Selection 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 Chapter 2 Literature Review page 2-1 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 Chapter 2 Literature Review page 2-2 Reproduction Strategy Of Labeobarbus Polylepis (Smallscale yellowfish) 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. Chapter 2 Literature Review page 2-3 Reproduction Strategy Of Labeobarbus Polylepis (Smallscale yellowfish) 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. Chapter 2 Literature Review page 2-4 Reproduction Strategy Of Labeobarbus Polylepis (Smallscale yellowfish) Several variations of the dry stripping techniques were tested on ripe running fish collected on the natural
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