Factors Influencing the Spawning Success of Oreochromis Karongae (Trewavas) in Ponds

Aquaculture Research. 1997. 28, 87-99

Factors influencing the spawning success of Oreochromis karongae (Trewavas) in ponds

O V Msiska SADC/UNAM Fisheries Planning and Management Course. University of Namibia, Windhoek, Namibia

B A Costa-Pierce Center for Regenerative Studies, California State Polytechnic University, Pomona. CA. USA

C orresp ond ence: Mr 0 V Msiska. SADC/UNAM Fisheries Planning and Management Course, University of Namibia. Private Bag 13 3 0 1 . Windhoek. Namibia

Genus Oreochromis, Subgenus Nyasalapia (Trewavas Abstract 1983). It is one of a closely related species complex Fry and fingerlings production of a pelagic tilapia group comprising Oreochromis lidole (Trewavas). 0. from Lake Malawi, Oreochromis karongae subgenus squamipinnis (Trewavas) and O. saka (Trewavas); the Nyasalapia (Trewavas), was lower (4.07 ± 5.09, last has been re-classified as a junior synonym of 0. 10-21 fry female-1 month"1) than reported for karongae (Turner & Robinson 1991). While these other tilapias (about 135 fry female-1 month-1). fish species share most characteristics, they are Although seasonality was very' pronounced in all known to segregate according to breeding depths, experimental systems, the use of net bags (hapas) substrate type and season (Lowe 1952). Oreochromis improved fry' yield to 24.7 ± 27.90, 0-354 fry karongae breeds at a wide range but in shallower female-1 month-1. Multiple regression analysis waters (0.5-28.0 m) than other species. Wild stocks demonstrated that the depth of ponds, solar grow relatively fast, attaining 12.0 cm (28 g). 22.0 radiation, rainfall and maximum temperature cm (1 8 9 g) and 2 7.5 cm (4 1 2 .5 g) in the first, second significantly influenced fry and fingerling production and third years, respectively (Trewavas 1983) in (adjusted R2 = 0.75: P = 0.0024). Injection of waters of low primary production (0.73 g C exogenous hormones intramuscularly (pimozide. m - 2 day- 1 ) (FAO 1991). Natural food consists LH-RHa) induced spawning and significantly (P < mostly of diatoms (Surirella, Melorira) (Mwanyama 0.05) improved spawning success to a maximum of 1992). Reproduction is not well studied but 998 fry female-1 month-1. preliminary findings indicate that total fecundity is As in other cultured tilapias. when placed in fine- 92-1100 (Lowe 1952: Mwanyama 1992). It is not meshed net bags, broodstock density was critical to known how many breeding cycles are achieved fry' production. A density of 1.0 fish m -2 for broodfish within a season although histological studies suggest of 120-200 g produced significantly larger numbers a trimodal distribution of active ova and fry of progeny in the hatchery system employed. production in ponds (Msiska 1996). Spawning was seasonal and restricted to This species complex, collectively known as November-February. Broodfish ponds given inputs 'chambo' in Malawi, has recently come under heavy of chicken layers' mash produced significantly (P < fishing pressure and overfishing in some areas of 0.05) higher numbers of fry and fingerlings than the south-eastern Lake Malawi (Turner 1996), maize bran (4.17 vs. 1.22 fry m-2 female-1 m onth- 1 ). resulting in escalating beach prices (GOM 1994). It has been suggested that artificial spawning and captive rearing of this species could enhance the Introduction fisheries and boost aquaculture, thereby easing the Oreochromis karongae (Trewavas) is a pelagic tilapia pressure on wild stocks. The natural reproductive species endemic to Lake Malawi and belongs to the biology was observed to be influenced by water

depth and climatic factors (Lowe 1952; Trewavas included: rows of teeth on the lower jaw, upper jaw 1983; Turner & Robinson 1991); however, these length, head length, lower jaw length, opercular 1, observations were not supported by experimental opercular 2, opercular 3, interorbital distance, depth data. at posterior of eye, maximum depth, depth at Spawning of Oreochromis (Nyasalapia) in captivity anterior of eye and pre-anal depth (Lowe 1952; has met variable success but appears feasible (Bern, Trewavas 1983; Turner, Pitcher & Grimm 1989). Chave & Peters 1978). The prospects for isolating The value of these characteristics in separating environmental parameters predisposing these fish to species/strains have been reported elsewhere (Msiska spawning have been enhanced by advances recently & Costa-Pierce, in press). Breeding males acquired made in applying multivariate analysis to tilapia yellow or white stripes along the dorsal and caudal growth (Prein, Hulata & Pauly 1993). It has been fins and females were dark but devoid of yellow or shown that most of the factors that explain growth white stripes. and spawning variance can simultaneously be identified through multiple regression analysis. Reproductive hormones have routinely been Effects of environmental and climatic employed in catfish and carp culture (Davy & variables Choiunard 1981; Pullin & Jhingran 1985) but, except for experimental purposes, their use in tilapias has been limited and mostly restricted to Climatic factors hybridization (Mires 1976, 1982). However, due to A selected number of environmental and climatic the altricial breeding behaviour, its popularity as a factors (temperature, hours of daily sunshine, solar food fish and its high market value, O. karongae may radiation and rainfall) were monitored at the be an ideal candidate for routine application of National Aquaculture Station, Domasi, Malawi, reproductive hormones. which records were supplemented by the Central Chicken layers' mash as a tilapia feed previously Meteorology Station. Blantyre, Malawi. Air and met with success on O. shiranus (Maluwa & Costa- water temperature profiles were obtained daily at Pierce 1993). Its suitability for O. karongae was the station using a maximum and minimum investigated with respect to spawning success. thermometer. Solar solarimeters measured incident Research into factors affecting tilapia hatchery and reflected radiation. Daily sunshine was systems is important to the growth of the monitored by a Campbell—Stokes recorder. aquaculture industry (Guerrero 1979; Beveridge 1984, 1987; Costa-Pierce & Hadikusumah 1990). In spite of this, no studies have considered inclusion Assessment of fry and fingerlings production of Lake Malawi pelagic tilapias, and the associated Fry and fingerlings were collected fortnightly from environmental factors implicated in spawning six ponds, measuring 500 m2 each, stocked at a 2:1 success have yet to be isolated. Thus, investigations female to male sex ratio. Broodfish ranged in size were made to underpin factors which are crucial to from 120 to 200 g and were fed a mixture of the reproductive success of Oreochromis karongae chicken layers’ mash (CLM, 15.8% crude protein) in captivity. and maize bran (MB, 9% protein) at 2.5% body weight per day (BWD). The total monthly production of fry and fingerlings is shown in Fig. 2. Materials and methods

Choice of broodfish Data analysis Environmental parameters were collated and re Parental stocks were obtained from the first filial arranged for multiple regression analysis (Table 1, generation of fish specimens caught at three sites below). Climatic variables were used as independent along the south-eastern section of Lake Malawi and variables while fry and fingerling numbers formed Malombe, between September 1989 and March the dependent variable. The equation used to explain 1990 (Fig. 1). The sites of broodfish collection were the variance around the regression line incorporated Cape Maclear, Kakoma Bay and Lake Malombe. several variables of the form (Zar 1984); The external morphometric and meristic

characteristics used in identifying the species V = a + b]*! + b2 * 2 + • . . + b„Kn + E

Figure 1 Sites on Lakes Malawi and Malombe used in the recruitment of Oreochromis karongae broodstock: A, Cape Maclear: B, Kakoma Bay; C. Lake Malombe.

Figure 2 Monthly fry production of Oreochromis karongae in ponds in 1991. Fish were stocked at 60 per 500 mJ in six ponds: food consisted of chicken layers' mash and maize bran at 2.5% body weight day-1 .

Table 1 Correlation of climatic variables1 and fry numbers of Oreochromis karongae raised in ponds at the National Aquaculture Centre. Domasi. Malawi, obtained by multiple regression analysis. Values marked * are significant at P < 0.05

Airmax Airmin Watmax Watmin Sunshine Radiation Rain Fry

Airmax 1.000 Airmin 0.771* 1.000 Watmax 0.914* 0.905* 1.000 Watmin 0.904* 0.825* 0.950* 1.000 Sunshine -0.430 -0.458 -0.495 -0.406 1.000 Radiation 0.738* 0.522 0.694* 0.735* 0.199 ' 1.000 Rain 0.793* 0.778* 0.754* 0.691* -0.847* 1.000 1.000 Fry 0.585* 0.342 0.461 0.406 -0.457 -0.132 0.491 1.000

'Abbreviated as follows: airmax, maximum air temperature: airmin. minimum air temperature; watmax, maximum water temperature; watmin, minimum water temperature; sunshine, daily sunshine hours: radiation, solar radiation; rain, rainfall; fry, fry/fingerling production in ponds.

where Y is the dependent variable, a is a constant, the predictor variables. Data were analysed using bj, bi, . . . b„ are the variable coefficients, Xj, x2, Microstat Software (Ecosoft, Inc., USA). ■ ■ ■ xn are the independent variables and E is the residual. The dependent and independent variables Effects of physical, chemical and nutritional were simultaneously analysed using an equation of factors the form:

(F2 ~ Fi)/(t2 - tx) = a + b^! + b 2x2 + . . . - + b„x„ Influence of pond depth on spawning success where F is the total number of fry/fingerlings at Two ponds, each 500 m2 and 1.25 m deep, were respective times, tx and t2. and Xj, x2 ■ ■ ■ x„ are stocked with 40 females of 149.0 ± 36.6 g and 20

Month Month

j i t JFKAHJJAS Month Month Month

Figure 3 Solar radiation recorded at Domasi in 1991/92 (Meteorological Services 1992. unpublished data).

Figure 4 Rainfall recorded at Domasi in 1991/92 (Meteorological Services. Malawi 1992. unpublished data).

Figure 5 Average minimum and maximum air temperature. Domasi (Meteorological Services, Malawi 1992. unpublished data).

Figure 6 Average maximum and minimum water temperature. Domasi 1991/92.

Figure 7 Sunshine hours at Domasi in 1991/92 (Meteorological Services. Malawi 1992. unpublished data).

males of 163.4 ± 44.2 g (mean ± SD). Another set repeated over 170 days at two different times of the of shallower ponds (500 m2 and 0.80 m deep) was year, in August 1991 to April 1992 and January stocked with the same number of fish weighing to June 1 9 9 3 . Broodfish were fed daily 6 days per 1 8 4 .8 ± 51.1 g for females and 2 0 5 .8 1 6.1 g for week using CLM at 2.5-3.0 % BWD. Fry and males. All the fish were fed CLM at 3% BWD. fingerlings were removed and counted fortnightly. Fry and fingerlings were removed and counted Data were analysed using a t-test. fortnightly. Data were analysed by the Wilcoxon signed test after establishing that normal distribution Effects of artificial hormones (pimozide, LH-RHa) on was not obeyed (Zar 1984). fry and fingerling production in net bags

Effects of broodstock density Six females and three males averaging 272.8 ± 37.1 g were stocked in each net bag. An injection Twelve, 3mX3mXlm nylon net bags (hapas) of 5 (Xg kg'1 LH-RHa was administered to all females of 1.6 mm mesh size, were suspended onto bamboo while males were given half the dosage, after a poles and staked at 0.8 m depth in a 500 m2 pond. priming injection of 5 mg kg "1, pimozide was given The following treatments were used and replicated to all experimental fish. Six net bags of 3 m X 3 m two times: 4 females: 2 males, averaging 144.3 + 20.9 g; X 1 m were used, half of which were experimental 6 females: 3 males, averaging 145.1 ± 49.2 g; and half control. Control females were injected with 10 females: 5 males, averaging 140.5 ± 49.2 g. saline solution. The experiment was conducted for Stocking densities used encompass those over 150 days from September 1992 to February recommended by Behrends & Lee (1990) for 1 9 9 3 . Oreochromis niloticus (L.) and by Maluwa & Costa- A salt solution (8% w/v) was administered as a Pierce (1993) for 0. shiranus. The experiment was general prophylaxis to all broodfish during handling.

Table 2 Multiple regression models of fry production in earthen ponds. Partial regression coefficients marked *, are significant at P < 0.1. P < 0.5 and P < 0.01, respectively

Independent variables b SE Beta

MODEL 1

Maximum air temperature 1091.6— 215.9 3.0 Solar radiation -14.5** 3.16 - 1 .7 Rainfall - 1 5 . 0 ” 4 .27 - 1 . 5

Constant -8 2 3 6 .1 Adjusted R2 0 .7 5 ” F value 12.06 Probability 0 .0024 Durbin—Watson test 1.7005

MODEL 2

Maximum air temperature 1128.3*** 195.3 3.1 Minimum air temperature - 1 9 4 .4 * 9 1.5 - 0 . 7 Maximum water temperature 355.8* 166.9 1.4 Minimum water temperature -263.0 178.1 -0.7 Solar radiation -1 5 .9 * ** 2.9 - 1 . 9 Rainfall - 1 6 .8 * ** 3.9 - 1 .6

Constant - 8 1 1 3 .4 Adjusted R2 0 .7 8 ” F value 9.23 Probability 0.014 Durbin-Watson test 1.7864

Fry and fingerlings were removed fortnightly and Effects of types of feed inputs data were analysed using a £-test. Broodfish weighing 143.5 ± 19.6 g and 104.3 ± 20.9 g (females and males, respectively) were stocked Water quality in broodstock ponds and net bags in four ponds. Each pond (500 m2, 1.25 m deep) was stocked at a density of 60 fish. Two ponds were In order to determine which microenvironmental given CLM while the other two were fed MB at 3.0% effects influence reproduction in net bags, chemical BWD until an average weight of 200 g after which analyses were conducted four times during the feed input was adjusted downwards to 2.5% BWD. experimental period. Analytical procedures for water Fry and fingerlings were removed fortnightly using chemistry followed standard methods (APHA 1989). a seine net. Data were analysed using a t-test. Conductivity was determined by a portable conductivity bridge (p310 model, YSI meter. USA) and pH was determined on unfiltered samples with a portable (Horiba) meter. Total alkalinity was Results estimated titrimetrically after filtration of samples Climatic and environmental variables through no. 3 filter pads using phenolphthalein and a mixed indicator. Dissolved oxygen was analysed Environmental measurements are shown in Figs 3 by a DO (YSI) meter, and ammonia was estimated 7. Solar radiation showed a decline between April by the Nessler technique incorporated in the Hach and August and was at a maximum in DREL/2 kit (Boyd 1 9 9 0 ). The perchloric acid November-February. Air and water temperatures digestion method was used for determining total followed the same pattern as solar radiation, with phosphorus (Golterman 1971). lowest temperatures in July and maxima in

Table 3 Mean (and standard deviation) of water quality parameters in earthen ponds and hapas. Values marked * are significantly different at P < 0 .0 5 using the Wilcoxon signed-rank test. Comparisons were carried out vertically on final values

Date Hapa/ PH Conductivity Alkalinity Dissolved Ammonia Phosphorus pond (mg I ' 1) (mg r 1) oxygen (mg r 1) (mg I" 1) (mg I ' 1)

06 Sep. 1991 Hapa 7.2 (0.2) 19.7 (0.2) 8.8 (1.0) 5.8 (0.2) 6.0 (0.02) 2.8 (0.2) Pond 6.5 (0.2) 33.6 (5.7) 8.0 (0.0) 6.4 (0.9) 0.7 (0.05) 0.8 (0.7)

29 Sep. 1991 Hapa 6.8 (0.06) 26.8 (0.3) 11.4 (5.0) 2.6 (0.3) 0.8 (0.06 2.8 (0.18) Pond 6.5 (0.0) 28.8 (2.4) 10.5 (3.5) 5.4 (0.2) 0.4 (0.11) 0.9 (0.1)

24 Oct. 1991 Hapa 6.9 (0.36) 31.8 (2.5) 7.9 (0.5) 1.5 (0.3) 0.7 (0.28) 0.4 (0.16) Pond 7.2 (0.71) 30.5 (2.7) 10.0 (0.00) 4.4 (0.21) 0.6 (0.02) 0.2 (0.02)

18 Feb. 1992 Hapa 5.5 (0.18)a* 30.3 (1.2)a* 17.3 (3.8)a 1.0 (0.2)a* 0.7 (0.05)a 0.4 (0.28)a* Pond 7.6 (0.24)b* 36.3 (2.3)b* 17.5 (3.5)a 3.8 (0.92)b* 0.8 (0.4)a 0.8 (0.4)b*

Table 4 Fry and fingerling production of Oreochromis karongae raised in shallow (0.8 m) and deep (1.25 m) ponds at the National Aquaculture Centre. Domasi. Malawi. Each value is an average of two replicates and values marked * are significantly different at P < 0.05 compared horizontally

Date Number of fry and fingerlings

Deep ponds Shallow ponds

Total m~2 mo. 1 Female 1 mo. 1 Total m 2 m o .'1 Female*1 mo. 1

Feb. 1991 457 0.46 5.71 170 0.17 2.13 Mar. 11 0.01 0.14 1 159 1.16 14.49 Apr. 906 0.91 11.33 513 0.51 6.41 May 457 0.46 5.71 250 0.25 3.13 June 210 0.21 2.63 47 0.05 0.59 July 0 0.00 0.00 262 0.26 3.28 Aug. 95 0.10 1.19 62 0.06 0.78 Sep. 12 0.01 0.15 47 0.05 0.59 Oct. 245 0.25 3.06 123 0.12 1.54 Nov. 590 0.59 7.38 56 0.06 0.70 Dec. 2523 2.52 31.54 860 0.86 10.75 Jan. 1992 1372 1.37 17.15 1 283 1.28 16.04 Feb. 176 0.18 2.20 303 0.30 3.79 Mar. 534 0.53 6.68 137 0.14 1.71 Apr. 848 0.85 12.50 470 0.47 5.88 May 1651 1.65 20.64 570 0.57 7.13 June 765 0.77 9.56 521 0.52 6.51 July 85 0.09 1.06 82 0.08 1.03

Total 10 937 10.96 138.63 6 915 6.91 86.48 Range 0-2 523 47-1 283 Mean 608* 0.61* 7.70* 384* 0.38* 4.80* SD 671 0.67 8.44 380 50.38 4.75

December-February. Hours of daylight were fewest Influence of artificial hormones on fry and in January and most in October. fingerling production A correlation matrix for all variables is given in Although hormonal injection started in August, no Table 1. used to determine parameters with low fry or fingerlings were observed until November. multicollinearity (Zar 1984) for the construction of Spawning peaked in November-February while the multiple regression models. Using Ecosoft Softwares, control recorded the highest output in November- plots of residuals were used to observe patterns and December. Thus, hormones extended the spawning the digression from the zero mean error. period by 2 months. The difference in fry' and There was a significant positive correlation (P < fingerling production between control and 0.01) between production of fry and fingerlings as experiment was significant (P < 0.05, (-paired the dependent variable and rainfall, radiation and test; Table 8). maximum air temperature as independent variables (adjusted R2 = 0.75, P < 0.0024, Durbin-Watson test = 1.7005) (Tables 2, 3). Minimum air and water temperatures had significant negative impacts Effects of feed on fry and fingerling on fry and fingerling numbers (Table 2). production Differences of dissolved oxygen and total Total fry and fingerling production was significantly phosphorus values between open ponds and net higher (P < 0.05, t-test) in the chicken layers' bags were significant (P < 0.05, Wilcoxon signed- mash (5 3 3 6 ) than in the maize bran (1 8 3 0 ) feed rank test). There was deterioration of pH with time treatments (Table 9). Seasonality of spawning was as acidity increased from 7.2 to 5.5. This difference reflected by high standard deviations. was significant after 162 experimental days (Table 3). Discussion

Effects of pond depth on spawning success From the time it was suggested that Oreochromis karongae might be a good candidate for aquaculture Fry and fingerling production in ponds of 1.25 m (Msiska, in press), many studies have been conducted and 0.80 m depth was significantly different (P < to demonstrate its good growth traits in ponds 0.001; Wilcoxon signed-rank test. Table 4). Both (Maluwa, Brooks & Rashidi 1995; Msiska & Costa- methods of expressing fry production, either as fry Pierce, in press). This tilapia species feeds low on the m '2 month-1 or as fry female-1 month-1 , showed food chain, preferring diatoms and other plankton a significantly higher production (P < 0.05) at (Lowe 1952; Fryer & lies 1972; Mwanyama 1992). the greater pond depth. Peak fry7 production was which partly satisfy its status as a candidate species recorded in November—March with a subsidiary suitable for aquaculture. What these studies did peak in May. Broodfish grew at a specific growth not, however, establish is whether' or not it can rate of 0.28-0.54% . The highest production was successfully be spawned in captivity and which recorded from broodfish of 6.0-6.6 tooth rows on environmental factors are critical in reproduction. the lower jaw (Table 5). The spawning studies generally confirmed evidence reported by Lowe (1952) for the Lake Malawi Nyasalapia species, who recorded very few (fewer Influence of broodstock density on spawning than 50 swim-up fry) in the mouth of brooding success females. This leads to the general conclusion that The highest level of spawning was recorded in this fish follows an altricial breeding behaviour not November—December with a small peak observed usually associated with tilapias. This behaviour was in February—March (Tables 6, 7). In both trials, a observed in all breeding experiments and was broodstock density of 1.0 fish m-2 yielded corroborated by histological studies (Msiska 1996), significantly (P < 0.05) higher production of fry which show that not all ovarian eggs are at the and fingerlings than a density of 0.7 fish m-2 . The same stage of development at any one moment. decline in spawning when broodfish were stocked Spawning is thus unlikely to occur at the same time at 1.7 fish m-2 was significant (P < 0.05) in the for all ovarian eggs. Unlike other tilapias used in second but not in the first experiment. aquaculture, confinement of O. karongae did not

Table 5 Mean stocking (MBW1) and harvesting (MBW2) body weights, daily gain and specific growth rates (SGP%). feed conversion ratios (FCR), spawning efficiency, lower jaw tooth rows and yield characteristics of Oreochromis karongae in deep (1.25 m) and shallow (0.80 m) earthen ponds

Deep ponds Shallow ponds

1 2 1 2

No. of broodfish 20(5 405 20 6 405 20 cj 405 20

Tooth rows on lower jaw Mean 6.6 7.0 6.0 5.8 SD 1.2 1.4 0.7 0.7 Max. 8 10 7 8 Min. 5 5 5 5 Sample no. 20 18 46 37 aAll ponds received layers' mash as the feed type.

Table 6 Fry and fingerling production from ponds stocked at three densities (0.7. 1.0. 1.7 fish m of Oreochromis karongae in J m X 3 m X 1 m hapas. Each density was replicated twice at two different times and means marked * are significantly different at P < 0.05 compared horizontally

-1 Month Total production Fry m 2 mo. Fry female 1 mo. 1

0.7 m~2 1.0 m 2 1.7 m 2 0.7 m”2 1.0 m-2 1.7 m“2 0.7 n r 2 1.0 m 2 1.7 n r 2

Aug. 0 0 0 0 0 0 0 0 0 Sep. 0 0 0 0 0 0 0 0 0 Oct. 0 0 8 0 0 6.0 0 0 6.0 Nov. 22 212 258 18.3 177 216 42.0 273 195 Dec. 2 6 11 1.86 6.2 9.3 3.1 9.3 24.5 Jan. 0 0 18 0 0 15.5 0 0 15.5 Feb. 6 28 112 4.9 8.7 89.9 11.6 29.0 81.2 Mar. 0 273 8 0 236 6.2 0 354 3.1 Apr. 0 41 16 0 33.0 12.0 0 52.7 12.4 May 0 18 7 0 1.5 6.0 0 24.0 6.2 June 0 0 96 0 0 83.7 0 0 74.4

Total 30 578 534 Mean 53 49 3* 42* 41* 6* 68* 38* SD 96 80 6 83 67 12.7 124 59

Table 7 Fry production from three stocking densities (0.7. 1.0, 1.7 m 2) of Oreochromis karongae in 3 X 3 X 1 m hapas. Each value is from three replicates and significant differences are marked * to denote P < 0.05 compared horizontally

Period Fry m 2 day-1 Fry female"1 day-1 Total fry production Mo. Day

0.7 m ”2 1.0 m 2 1.7 m-2 0.7 m 2 1.0 m~2 1.7 n r 2 0.7 m 2 1.0 m"2 1.7 m~2

Jan. 0 0 0 0 0 0 0 0 0 0 Feb. 47 0.15 3.75 0.93 0.33 4.88 0.83 4 84 25 Mar. 75 0.04 5.57 0.39 0.08 7.17 0.20 1 301 10 Apr. 120 0.00 1.93 0.26 0.00 2.48 0.33 1 104 10 May 138 0.00 0.04 0.04 0.00 0.05 0.03 0 2 1 June 176 0.10 0.48 0.04 0.25 0.62 0.03 3 26 1

Total 517 47 Mean 0.04 1.46 0.28 0.11 2.53 0.34 2 87 8 SD 0.06 2.13 0.35 0.11 2.94 0.31 2 114 10

Table 8 Fry and fingerling production of Oreochromis karongae in 3 X 3 X 1 m hapas stocked at a ratio of 1:2 (male to female) using broodfish of 2 0 0 -2 5 0 g average weight (0.5 kg m~2). Each hapa held 6 females and 3 males, injected with 5 mg kg-1 pimozide and 15 |ig kg-1 D-Ala-LH-RHa. Vertical comparisons marked * are significant at P < 0.05

Treatment* Experimental day Month Fry m 2 Fry female 1 day"1 Total production

LH-RHa 0 Sep. 0 0 0 15 Sep. 0 0 0 43 Oct. 0 0 0 60 Nov. 27.2 42.9 733 90 Dec. 6.4 9.7 174 109 Dec. 30.5 45.8 824 128 Jan. 27.2 42.9 733 158 Feb. 26.7 40.1 721

Total 118 182 3185 Mean 14.8* 22.7* 399* SD 14.3 21.9 384.6

Control-saline 0 Sep. 0 0 0 15 Sep. 0 0 0 43 Oct. 0 0 0 60 Nov. 27.0 41.0 728 90 Dec. 4.6 6.8 124 109 Dec. 0 0 0 128 Jan. 0.1 0.1 2 158 Feb. 0.2 0.2 4

Total 31.8 47.7 858 Mean 4.0* 6.2* 107.3* SD 9.4 14.0 254.5

“Source of hormones: Sigma Chemical Co. Full names: Pimozide: D-Ala luteinizing-hormone-releasing hormone.

lead to precocious spawning, and seasonality was generally obtained in other tilapias (14.5 vs. 135 strongly maintained. The production of fry and female'1 month-1; Costa-Pierce & Hadikusumah fingerlings obtained in this study was lower than 1995).

Table 9 Fry production of Oreochromis karongae from broodfish fed chicken layers' mash and maize (Zea mais) bran in ponds. Each treatment is replicated three times and significant differences are marked * at P < 0 .0 5 compared horizontally

Date Number of fry and fingerlings

Maize bran feed Chicken layers' mash feed

Total m 2 mo. 1 m "2 fem ale'1 Total m '2 mo.-1 m "2 female 1

Jan. 1991 64 0.06 0.80 208 0.28 2.60 Feb. 0 0.00 0.00 170 0.17 2.13 Mar. 155 0.16 1.94 1159 1.16 14.50 Apr. 538 0.54 6.73 513 0.51 6.42 May 224 0.22 2.8 250 0.25 3.13 June 0 0.00 0.00 47 0.05 0.60 July 32 0.03 0.40 262 0.26 3.28 Aug. 11 0.01 0.14 62 0.06 0.78 Sep. 4 0.00 0.05 47 0.05 0.59 Oct. 1 0.09 0.02 123 0.12 1.54 Nov. 93 0.20 1.16 56 0.06 0.70 Dec. 196 0.10 2.45 675 0.68 8.44 Jan. 1992 101 0.15 1.26 999 1.00 12.50 Feb. 148 0.03 1.85 180 0.18 2.25 Mar. 31 0.02 0.39 117 0.12 1.46 Apr. 21 0.17 0.26 453 0.45 5.66 May 165 0.04 2.06 450 0.45 5.63 June 2 0.00 0.53 483 0.45 6.04 July 4 0.00 0.05 82 0.08 1.03

Total 1830* 1.83 22.89 5336* 6.41 79.25 Mean 97 0.10* 1.22* 281 0.34* 4.17* SD 130 0.13 1.62 255 0.32 4.03

The use of net bags improved fingerling production the spawning experiments confirms that climatic over earthen ponds from a maximum of 32 to factors are critical to maturation. Many studies on 216 fry female-1 month-1. However, such high natural tilapia populations have alluded to these spawning was seasonal and of a very short duration, observations (Welcomme 1967; Siddiqui 1977), but lasting for about 2 months except when artificial none have actually quantified the effects on hormones were employed. Stocking broodfish of reproductive success. Manipulating climatic factors 120-200 g at a density of 1.0 fish m-2 produced could improve spawning success as is commonly significantly more fry and fingerlings than other practised for carps (Pullin & Jhingran 1985). Under densities (0.7 and 1.7 fish m-2 ). An explanation for controlled hatchery conditions, manipulating this may be inferred from a related experiment in physical and chemical variables might give an option which it was shown that 0. karongae has lower for obtaining higher number of offspring from 0. tolerance limits to dissolved oxygen (50% mortality karongae. Rainfall has been implicated in the was recorded at 5 mg l-1 ) than either O. niloticus reproduction of carps. For example, fluctuating or O. shiranus (Msiska 1996). water levels are used to induce the fish to breed Regression models developed to explain monthly (Huet & Timmermans 1986). fry and fingerling variation showed a strong Irrespective of whether earthen ponds or net bags correlation (P < 0.01) between fry and fingerling were used, peak spawning occured in production (as a dependent variable) and rainfall, November-February. There was a subsidiary peak radiation and air temperature (as independent in March—May and June-July but inconsistent variables). The strong seasonality observed in all results need further investigations. The strong

seasonality in breeding behaviour displayed by O. enhance its nutritive value (Kadongola 1990; karongae under captive conditions is in marked Maluwa 1990). contrast to other tilapias, which spawn easily when water temperatures are above 22°C (Jalabert & Zohar 1983). Acknowledgments Multiple regression analysis was shown to be a powerful tool for determining simultaneous effects This study was funded by the ICLARM/GTZ Africa Aquaculture Project based in Malawi. Dr Roger Puilin of environmental parameters on reproduction that assisted in securing funds for the study. Valuable comments can be used in the choice of hatchery technology. on formulation of hypotheses were made by Dr A Eknath The models developed and relationships elaborated (ICLARM. Philippines). Dr A S Grimm kindly supplied the are exploratory and need to be confirmed pimozide hormone used in the hormone experiment. Advice experimentally (Prein et al. 1993). Unexplained on the analytical techniques was given by Drs M Prein and A van Dam of ICLARM. Parent fish collections were variation of about 0.25 in reproduction may be made possible through IDRC funding (Fish Polyculture due to factors not considered in the study. The Project). importance of water depth to spawning success suggests a role for pressure or light intensity in the reproduction of 0. karongae. This corroborates References previous studies by Lowe (1952), Trewavas (1983) and Turner & Robinson (1991). Failure to modify APHA. (American Public Health Association) (1989) this in captivity suggests a strong genetic basis for Standard Methods for the Examination of Water and Waste this trait. Water, 17th edn. American Water Works Association Injection of pimozide and LH-RHa, as priming and and Water Pollution Control Federation. Washington resolving hormones, was successful in increasing DC. USA. 1467 pp. Behrends L.L. & Lee J.C. (1990) Hatchery systems for spawning. These hormones, however, failed to tilapia. In: Proceedings of Auburn University Symposium change the period for the onset of maturation, on Fisheries and Aquaculture (ed. by R.O. Smitherman & although they substantially raised production to a D. Tave), pp. 61-71. Alabama Agricultural Station. maximum of 998 fry female-1 month-1. The Auburn University. AL. USA. duration of spawning was also extended by 2 Bern S.. Chave E.H. & Peters H.M. (1978) On the biology months, an indication that oocytes that fail to spawn of Tilapia squamipinnis (Gunther) from Lake Malawi under natural conditions can be induced artificially. (Teleostei: Cichlidae). Archiv fuer Hydrobiologie 84, There is need to conduct further experiments and 2 1 8 -2 4 6 . for a longer duration so that the full potential of Beveridge M.C.M. (1984) Lake based or land-based tilapia hormones during an annual cycle may be known. hatcheries? ICLARM Newsletter 7(1). 10-11. Considering the low level of natural spawning Beveridge M.C.M. (1987) Cage Aquaculture. Fishing News Books, Farnham, Surrey, England. UK. 352 pp. success, routine administration of hormones may Boyd C.E. (1990) Water Quality in Ponds for Aquaculture. be a practical option in increasing fiy production. Alabama Agriculture Experiment Station. Auburn Our experiments show that, for optimum results, University. Birmingham Publishing Co., Alabama, USA, many factors have to be manipulated simul 227 pp. taneously, including careful broodfish selection as Costa-Pierce B.A. & Hadikusumah H.Y. (1990) Research suggested by differences in spawning success on cage aquaculture systems in the Saguiling Reservoir, associated with tooth rows of the lower jaw. Whether West Java, Indonesia, in: Reservoir Fisheries and or not this phenotypic characteristic has a genetic Aquaculture Development for Resettlement in Indonesia (ed. basis and how it is associated with other key by B.A. Costa-Pierce & 0. Soemarwoto), pp. 112-217. reproductive indicators remains to be investigated. ICLARM Technical Reports 2 3 , ICLARM, Manila, As expected, chicken layers’ mash was superior as Philippines. Costa-Pierce B.A. & Hadikusumah H.Y. (1995) Production a feed compared with maize bran with respect to management of double net tilapia (Oreochromis spp.) reproductive success. Although the mash is more hatcheries in a eutrophic tropical reservoir. Journal o f costly, the magnitude of the spawning difference the World Aquaculture Society 26, 4 5 3 -4 5 9 . more than compensates for this cost and the feed Davy F.B. & Chouinard A. (eds) (1981) Induced fish amounts involved are minimal. Not only does breeding in south east Asia: report of a workshop held chicken layers' mash contain a higher level of in Singapore, 2 5 -2 8 November 1980, IDRC, Ottawa, protein, it is reportedly fortified with minerals which Canada, 48 pp.

FAO. (1991) Chambo fisheries research: preliminary note Oreochromis karongae in ponds and open waters in Malawi. on the decline of Chambo in Lake Malombe. FD/GOM/ PhD thesis. University of Malawi. FAO/UNDP/MLW/86/013. Msiska O.V. (in press) The potential for aquaculture of Fryer G. & lies T.D. (1972) The Cichlid Fishes of the Lake Malawi tasselled Oreochromis subgenus Nyasalapia. Great Lakes of Africa: Their Biology and Evolution. TFH In: The Asian Regional Workshop on Tilapia Genetics (ed. Publications, Neptune City. NJ. USA, 641 pp. by A.E. Eknath & R.S.V. Pullin). ICLARM Conference GOM (Government of Malawi, Fisheries Department) Proceedings. Manila. Philippines. (1994) Beach Prices Summary of 1990-1993 and Price Msiska O.V. & Costa-Pierce B.A. (in press) Growth Forecasts from 1994. Prepared by S.J.R. Bland. Fisheries performance of Oreochromis Mole, Oreochromis Bulletin No. 17. squamipinnis, Oreochromis shiranus and Oreochromis Guerrero R.D. Ill (1979) Cage culture of tilapia in the karongae. new candidate fish species for aquaculture Philippines. Asian Aquaculture 2, 6. in open waters and fish ponds. ICLARM Conference Huet M. & Timmermans J.A. (1986) Textbook for Fish Proceedings. 4 1 . Culture: Breeding and Cultivation of Fish. 2nd edn. Fishing Mwanyama N.C. (1992) Feeding and fecundity of the News Books, Farnham, Surrey. UK, 4 3 8 pp. Chambo species. GOM/FAO/UNDP/MLW/86/013. Jalabert B. & Zohar U. (1983) Reproductive physiology in Technical Summary Paper No. 3. 10 pp. cichlid and Sarotherodon. ICLARM Conference Proceedings Prein M., Hulata G. & Paouly D. (1993) Multivariate 7, 1 2 9 -1 4 0 . methods in aquaculture research: case studies of tilapia Kadongola W.K. (1990) Maize (Zea mais Linnaeus) bran as in experimental and commercial systems. ICLARM Study supplemented feed in the culture o f Tilapia rendaili Review 20. 221 pp. (Boulenger) and Oreochromis shiranus sp. (Boulenger). Siddiqui A.Q. (1977) Reproductive biology, iength-weight MSc thesis. University of Malawi. condition of Tilapia leucosticta (Trewavas) in Lake Lowe R.H. (1952) Report on the tilapia and other fish and Naivasha, Kenya. Journal of Fish Biology 10, 251-260. fisheries of Lake Nyasa, 1945^17. Fish Publ. Colon. Off. Trewavas E. (1983) The Hlapiine Fishes of the Genera Lond. 1(2): 126 pp. Sarotherodon, Oreochromis and Danakilia. British Museum Maluwa A.O.H. (1990) Reproductive biology and fry (Natural History), London. production of Oreochromis shiranus. MSc thesis, Turner G.F., Pitcher T.J. & Grimm A.S. (1989) Identification University of Malawi. of Lake Malawi Oreochromis (Nyasalapia) spp. using Maluwa A.O.H. & Costa-Pierce B.A. (1993) Effect of multivariate morphometric techniques. Journal of Fish broodstock density on Oreochromis shiranus fry Biology 35, 799-812. production in hapas. journal of Applied Aquaculture 2. Turner G.F. & Robinson R.L. (1991) Ecology7, morphology' 6 3 -7 6 . and taxonomy of Lake Malawi Oreochromis (Nyasalapia) Maluwa A.. Brooks A. & Rashidi B. (1995) Production of species flock. Annales du Musee Royal de I’Afrique Central the Malawi chambo, Oreochromis karongae association, (Servie in 8vo. Sciences Zoologiques) 262. 23-28. and Oreochromis shiranus in polyculture with the African Turner G.F. (1996) Fishing and the conservation of catfish. Aquaculture Research 26, 103-108. endemic fishes of Lake Malawi. In: Speciation in Ancient Mires D. (1977) Theoretical and practical aspects of the Lakes (ed. by K. Martens. B. Goddeeris & G. Coulter). production of all male Tilapia hybrids. Bamidgeh 29(3), Arch. Hydrobiol. Beih Ergebn Limn. 4 4 . 4 8 3 -4 9 6 . 9 4 -1 0 4 . Welcomme R.L. (1967) The relationship between fecundity Mires D. (1982) The study of the problem of mass and fertility' in mouth brooding cichlid fish. Tilapia production of hybrid tilapia fry. ICLARM Conference leucosticta. Journal of Zoology 151, 453-468. Proceedings 7, 317-329. Zar J.H. (1984) Biostatistical Analysis. Prentice Hall. Msiska O.V. (1996) Reproductive biology and growth of Englewood Cliffs. NJ, USA, 718 p.

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