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C. East Africa - PD/A CRSP 14 Annual Administrative Report
PD/A CRSP Fourteenth Annual Administrative Report
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IV. Abstracts of Technical Reports

C. East Africa Abstracts

Masculinization of Tilapia through Immersion in 17a-Methyltestosterone or 17a-Methyldihydrotestosterone

Interim Work Plan, Africa Study 2

Martin S. Fitzpatrick, Carl B. Schreck, and William L. Gale
Oregon Cooperative Fishery Research Unit
Oregon State University
Corvallis, USA

Abstract

The use of all-male populations increases the efficiency and feasibility of tilapia aquaculture. The objective of this study was to determine the efficacy of a short term immersion procedure for masculinizing Nile tilapia (Oreochromis niloticus). Two synthetic androgens were evaluated, 17a-methyldihydrotestosterone and 17a-methyltestosterone. Three-hour exposure of fry at 10 days and 13 days post-fertilization in methyldihydrotestosterone at 500 mg/l produced sex ratios greater than 93% male. Immersions in methyldihydrotestosterone at 100 mg/l and methyltestosterone at 500 mg or 100 mg/l were unsuccessful at producing all-male populations. Immersion of Nile tilapia in 500 mg/l methyldihydrotestosterone may provide a practical alternative to the use of steroid-treated feed. Furthermore, when compared with current techniques for steroid-induced sex inversion of tilapia, short term immersion shortens the treatment period and reduces the risk of worker exposure to anabolic steroids.

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Experimental Evaluation of Lime Requirement Estimators for Global Sites

Interim Work Plan, Africa Study 3

James R. Bowman and Wayne K. Seim
Department of Fisheries and Wildlife
Oregon State University
Corvallis, USA

Abstract

Artificial enclosures ("isolation columns") were constructed and placed in an earthen pond to investigate their utility as test units for pond treatments and to com-pare results with results obtained from a series of experi-ments designed to evaluate alternative lime requirement determination methods in laboratory microcosms. Six 30-cm diameter columns were placed in the pond at depths of approximately 1 m. Three units were treated with agricultural limestone at a rate calculated to completely neutralize soil acidity and three units remained untreated. Water column samples were taken from each isolation column and from the open pond adjacent to the columns and examined for total alkalinity after 1, 3, 7, 14, 21, and 28 days. Bottom soil from the same pond was used to conduct parallel treatments in 800-ml laboratory micro-cosms. Total alkalinities in the open pond and in unlimed columns remained relatively low throughout the experi-ment, and trends in unlimed columns were similar to those in the open pond, suggesting that the columns themselves had little effect on alkalinity. Alkalinities in the limed columns rose to almost 30 mg/l CaCO3 within 24 hours and continued to rise throughout the experi-ment, reaching approximately 50 mg/l by day 28. Alkalinities in unlimed laboratory microcosms rose initially, but declined to about 12 mg/l by the end of the experiment, whereas alkalinities in limed micro-cosms rose to over 60 mg/l by day 14 and then gradually declined, reaching about 52 mg/l by day 28. Alkalinity trends in both limed and unlimed micro-cosms differed noticeably from trends in pond enclo-sures, and significant differences were observed among all day-28 alkalinities except those in limed micro-cosms and limed isolation columns. This suggests that results in either the isolation columns or the micro-cosms or both may not be representative of the effects of liming in real ponds.

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Characterization of Soils from Potential PD/A CRSP Sites in east Africa

Interim Work Plan, Africa Study 4

James R. Bowman and Wayne K. Seim
Department of Fisheries and Wildlife
Oregon State University
Corvallis, USA

Abstract

Nine soil samples were collected from five potential PD/A CRSP research sites in East Africa during site evaluation visits in 1994 and 1995. Samples were returned to Oregon State University, where their physical and chemical composition was charac-terized. Clay contents ranged from 4.4% to 81.7%. Three samples were alkaline (pH 7.22-8.01), two were approximately neutral (pH 6.55-6.85), and four were acidic (pH 5.08-5.55). SMP lime requirements ranged from 0 kg to 10,898 kg/ha. Organic matter contents ranged from 0.25% to 6.31%. All but one of the sites would have been acceptable, in terms of soil quality, as PD/A CRSP research sites. Soil character-ization data were made available to supplement other information used in evaluating and selecting the new site for PD/A CRSP research in Africa.

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Effect of Feed Storage Time and Storage Temperature on Growth Rate of Tilapia Fry and Efficacy of Sex Reversal

Interim Work Plan, Africa Study 8

Edwin S. Smith and Ronald P. Phelps
Department of Fisheries and Allied Aquacultures
Auburn University
Auburn, USA

Abstract

Effects of storage conditions of methyltestosterone-treated feed on fish growth and sex reversal were evaluated. A common source of feed was treated with 60 mg methyltestosterone/kg, stored frozen, and then held under one of the following six conditions: 1.) 26 days at ambient conditions before use, 2.) seven days at ambient conditions before use, 3.) zero days at ambient conditions before use, 4.) two months at 4°C and zero days at ambient conditions before use, 5.) two months at 4°C and 7 days at ambient conditions before use, and 2 months at 4°C and 26 days at ambient conditions before use. These rations were fed to Oreochromis niloticus fry for 28 days. Fry with an initial length of 10.4 mm were stocked at 4,000/m3 in outdoor hapas and fed at 15%, 12%, 8%, and 4% body weight per day during weeks 1, 2, 3, and 4, respectively. Growth and survival were determined after the 28-d treatment period. Fry were reared to a minimum size of 4 cm. Fish were sexed using the gonadal squash technique and the percent of male, female, and intersex fish was determined. Feed storage conditions had no effect on the percentage of males produced. All hormone-treated feeds resulted in > 99% male populations. Storage conditions had no effect on growth, FCR, or fish survival when fish were treated in fertile fish ponds. Mean fish weight after 28-d of treatment was 0.9 g, FCR was < 1, and survival averaged > 55%.

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Reproductive Efficiency, Fry Growth, and Response to Sex Reversal of Nile and Red Tilapia

Interim Work Plan, Africa Study 6

Edwin S. Smith and Ronald P. Phelps
Department of Fisheries and Allied Aquacultures
Auburn University
Auburn, USA

Abstract

Reproductive efficiency, fry growth, survival, feed conversion, and sex reversibility of red tilapia, a synthetic breed derived from Oreochromis niloticus, Oreochromis aureus, and Oreochromis mossambicus, were compared with Nile tilapia Oreochromis niloticus. In four trials, brooders of red and Nile tilapia were stocked in separate ponds and allowed to spawn for 215 to 230 degree-days (13 to 19 days) using two ponds per fish type. A complete harvest of the pond to collect fry from the harvest basin was completed, and fry were graded ( 14 mm, > 14 mm) and enumerated. Fry (14 mm) from both types of brooders were stocked at 4000/m3 in outdoor hapas and given feed containing 60 mg/kg 17a-methyltestosterone. Hormone treatment periods were 0, 14, 21, and 28 days. After 28 days of confinement, fry were harvested and growth and survival determined. Fry were reared for an additional 58 days and the sex was determined using the gonadal squash method. Brood survival was similar for both types of fish (p < .05). There was no difference in the number of fry/kg of brood female produced by each fish type. Fecundity was directly correlated with temperature. Red x red brooders produced an average of 77% red and 23% wild-type (black) fry. There was no difference in the percent males obtained from hormone-treated fry of either parental line. Mean fry survival and growth was similar for fry of both red and Nile tilapia.

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African Site Evaluation and Development Planning

Interim Work Plan, Africa Study 1

Wayne K. Seim and James R. Bowman
Department of Fisheries & Wildlife
Oregon State University
Corvallis, USA

Thomas J. Popma and Karen L. Veverica
Department of Fisheries and Allied Aquacultures
Auburn University
Auburn, USA

Abstract

Under Work Plan 7, Study C, a site selection strategy was developed to begin the process of replacing the site at Rwasave, Rwanda. That site was lost because of the outbreak of war and civil violence in 1994. The following outlines the site-selection strategy employed:

Fifteen site evaluation criteria were developed with assistance from the ME and Technical Committee of the Pond Dynamics/Aquaculture (PD/A) CRSP to guide data collection. USAID site-selection criteria were incorporated into the process. Under the current study, additional site visits were accomplished and developed into formal evaluations. The Sagana Fish Culture Farm in Kenya was recommended as a prime site during the PD/A CRSP Annual Meeting in January, 1996. Once approved, a proposal to develop a CRSP site at Sagana in cooperation with the Kenya Ministry of Tourism and Wildlife and its Department of Fisheries was submitted to the government of Kenya. A development plan for that station was also outlined. The government of Kenya, through the Ministry of Treasury and the Ministry of Tourism and Wildlife, recently approved our preliminary proposal and invited the Africa PD/A CRSP Project to submit a Memorandum of Understanding to formalize working relationships at Sagana Fish Culture Farm.

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Gonadal Differentiation in Nile Tilapia as a Function of Growth Rate and Temperature

Interim Work Plan, Africa Study 7

Joyce R. Newman
Department of Fisheries and Allied Aquacultures
Auburn University
Auburn, USA

Abstract

Research on, and actual on-farm use of 17a-methyltestosterone to masculinize tilapia fry has been conducted for many years. While it has been logically inferred that the presumptive gonad in Oreochromis niloticus differentiates at some time during the first 28 days of feeding, research data supporting this has been somewhat inconclusive. It is also not known what effect water temperature and growth rate have on the process. These are crucial factors, since tilapia fry around the world grow at a very wide range of rates during this time period. In this study, Nile tilapia fry were reared at two temperatures (30° and 22°C) and two growth rates (fast and slow). Growth rates were achieved by using a "high" or "low" feed rate. At each temperature, the high ration approximated satiation based on preliminary data from a previous study, and fell at a rate of 15% every 4 days. The low ration on Day 0 was 1/4 the initial high ration and fell at 1/3 the rate (5% every 4 days). The feeding and sampling period was 28 days. Ten fish per day were randomly removed from one aquarium in each treatment and preserved. Preserved fish will be embedded in paraffin, sectioned, stained and mounted for microscopic examination of the gonads. To date, all fish samples have been collected and the histological work remains to be done. It is anticipated that the results of this work will benefit both tilapia producers and consumers by pinpointing the time at which hormone use is effective, thus resulting in a reduction of the amount needed for sex reversal.

Risk Analysis of Optimal Resource Allocation by Fish Farmers in Rwanda

Work Plan 7, Africa Study 7

Carole R. Engle
Department of Aquaculture and Fisheries
University of Arkansas at Pine Bluff
Pine Bluff, USA

Abstract

Although many small-scale fish farming projects around the world promote fish production as a source of low-cost protein, increasing evidence demonstrates that fish can be an important cash crop, even for resource-limited farmers. A mathematical programming model was developed from survey data collected with the help of Rwandan farmers to determine optimal resource allocation on subsistence farms in Rwanda. The specific objective of the study was to conduct an economic risk analysis of fish production on subsistence fish farms in Rwanda. At low levels of willingness to incur risk, the optimal product mix was to select those crops that had low variability in yield and those cash crop options with low coefficients of market risk. Explicit estimation of risk parameters in the model generated equivalent results to those of models specified to meet household nutritional requirements. Both approaches demonstrated the preference of subsistence farmers to select crops with stable, although sometimes lower, yields to maximize food security.

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Optimal Resource Allocations by Fish Farmers in Rwanda

Interim Work Plan, Africa Study 10

Carole Engle
Department of Aquaculture and Fisheries
University of Arkansas at Pine Bluff
Pine Bluff, USA

Abstract

Although many small-scale fish farming projects around the world promote fish production as a source of low-cost protein, increasing evidence demonstrates fish to be an important cash crop, even for limited-resource farmers. A mathematical programming model was developed from survey data of Rwandan farmers to determine optimal resource allocation on subsistence farms in Rwanda. The specific objective of the study was to determine farm plans that maximize returns to a representative Rwandan farm family's resources, subject to constraints of the farm family's proteinic and caloric requirements. The average land holdings for both individually- and cooperatively-managed farms were too low to meet the minimum nutritional needs of a family. Government policy makers should take into consideration that a minimum of 0.20 ha and 0.51 ha were required for individually- and cooperatively-managed farms, respectively, to meet household nutritional requirements. Fish production was a profitable enterprise for subsistence farmers in Rwanda, that competes well for scarce land resources. If fingerlings can also be sold, fish is the optimal cash enterprise across most regions and throughout the year in Rwanda. With-out a ready market for fingerlings, cabbage production was the profit-maximizing cash crop for the period from July through October when cabbage prices were high. However, from Novem-ber through June when cabbage prices were low, fish pro-duction even without fingerling sales was the cash crop that maximized profits. Regional price differences had less effect on optimal product mix than the seasonality of prices. The exception was the region closest to Kigali where high sweet potato prices in October provided an incentive for sweet potatoes to be raised as a cash crop. Soybeans, sweet potatoes, and maize were selected to meet household nutritional requirements. Fish production was selected as the principal cash crop, lending support to the evidence that fish is more important as a cash crop than as a primary protein source in Rwanda. Low-cost technologies that increase fish yield have significant positive impacts on net farm income.

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