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Africa


C. Africa

Binding Sites for the Masculinizing Steroid Mibolerone in the Gonadal Tissue of Adult Nile Tilapia (Oreochromis niloticus)

Work Plan 7, Egypt Study 4C1

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

Abstract

A binding site in the gonadal tissue of adult Nile tilapia (Oreochromis niloticus) was characterized using the synthetic androgen mibolerone (17-hydroxy-7,17-dimethylestr-4-en-3-one). The binding site demonstrated high affinity (Kd = 1.03 +/- 0.11 nM ; n=2) and low capacity (Bmax = 5.65 +/- 0.42 fmol/mg protein; n=2) for mibolerone binding. Furthermore, it was located in gonadal cytosol only. The binding site also demonstrated ligand specificity. Only steroids with sex inverting capabilities displaced tritiated mibolerone binding. The receptor assay developed for tilapia may represent an important tool for the screening of newly developed sex inversion agents.

Effects of Form of Defatted Rice Bran Offered on Nile Tilapia Production in Ponds

Peter W. Perschbacher and Rebecca Lochmann
Department of Agriculture
University of Arkansas
Pine Bluff, Arkansas, USA

Abstract

Mixed-sex Nile tilapia were stocked into each of six 0.04-ha earthen ponds at 2.3 fish/m2. Ponds were fertilized as necessary to maintain concentrations of chlorophyll a at approximately 100 mg/m3 and fish were fed defatted rice bran at 2% body weight per day, divided into two feedings. In half of the ponds fish were fed defatted rice bran as a loose product and in the remaining ponds fish were fed a pelleted form. Advanced largemouth bass fry were also stocked into all ponds at 0.15 fish/m2 to reduce tilapia reproduction. After 169 days ponds were drained and fish harvested. Net yields of stocked tilapia and reproduction were not significantly different between treatments and averaged 6128 kg/ha and 6316 kg/ha on an annual basis in pellet and loose fed treatments, respectively. Stocked fish averaged 100 and 90 g, respectively. Stocked fish yield was 13% higher in pellet-fed ponds. Maximum feeding was 45 kg/ha/d. Bass yield averaged 159 and 136 kg/ha in loose and pellet-fed ponds, respectively, and the average sizes were 236 g and 198 g. Chlorophyll a averaged 87.5 and 115 mg/m3 in loose and pellet-fed treatments, respectively. Fertilizer applications required were signifcantly different and averaged 15.3 and 23.0, respectively. Defatted rice bran appears to be a good and economic supplemental food source. Pellets have advantages over loose form in ease of handling. Pellets also reduced the number of fertilizer applications needed to maintain pond fertility, and it apparently promoted increased yields of large fish.

Effect of 17a-Methyltestosterone on the Growth of Two Tilapia Species, Oreochromis aureus and Oreochromis mossambicus, in Fresh Water

Work Plan 7, Egypt Study 4B1

N. Harold Richman III and E. Gordon Grau
Hawaii Institute of Marine Biology
University of Hawaii at Manoa
Kaneohe, Hawaii, USA

Abstract

We examined the effect of 17a-methyltestosterone (MT) on the growth of two tilapia species, Oreochromis aureus and Oreochromis mossambicus, reared in fresh water. The growth rate of O. aureus was nearly twice that of O. mossambicus at each dose level (0, 1, 10, and 25 mg of MT/kg of feed). With the exception of O. aureus treated with 1 mg of MT/kg of feed, MT treatment significantly increased (p < 0.01) growth in both species over control animals. In O. mossambicus, growth performance increased with increased levels of MT. By contrast, the 10 and 25 mg of MT/kg of feed treatments stimulated growth equally in O. aureus. The gonadosomatic index (GSI) was not significantly different between treatments within each species. It was, however, significantly lower (p<0.0001) in O. aureus than in O. mossambicus. Gonadal weights were not significantly different between species which suggests that the smaller GSI in O. aureus results, at least in part, from the larger somatic mass of the animals. In both species, the hepatosomatic index (HSI) and absolute liver weight tended to increase with increased levels of MT and were significantly greater ( p< 0.05; p < 0.01) in the 25 mg of MT/kg of feed treatment groups than in controls. The male-to-female sex ratio was not significantly different from 1:1 in any treatment group in either species. Analyses of residual MT levels in the serum and muscle samples are ongoing.

Use of 17a-Methyltestosterone for Tilapia Sex Reversal

Work Plan 7, Egypt Study 4A2

Bartholomew W. Green
Department of Fisheries and Allied Aquacultures
Auburn University, Alabama, USA

Esam H. Rizkalla and Abdel R. El Gamal
Central Laboratory for Aquaculture Research
Agricultural Research Center
Abbassa, Egypt

Abstract

The U.S. Food and Drug Administration granted a compassionate Investigational New Animal Drug (INAD) exemption to Auburn University, the American Tilapia Association, and a commercial feed producer to collect data to support a New Animal Drug Application for the use of 17a-methyltestosterone (MT) for sex reversal of newly-hatched tilapia. Implementation of a clinical field trial at research institutions and commercial tilapia production facilities throughout the United States and overseas was one activity contemplated under this INAD exemption. U.S. and Egyptian researchers involved with the Pond Dynamics/Aquaculture Collaborative Research Support Program participated in the field trial. The first trial was initiated on 10 to 12 July 1994 when Nile (Oreochromis niloticus) and blue (O. aureus) tilapia fry were stocked into treatment hapas. A second trial was initiated on 18 to 20 September 1994. Fry availability allowed for stocking of two hapas each for control and MT treatment per species. Fish in Trial I completed treatment on 8 to 11 August; sub-samples of control and treated fry were restocked into hapas for nursery growth. Trial II was in progress, with an expected treatment completion date of 16 to 18 October 1994. Upon completion of the Trial I treatment period, Nile tilapia averaged 0.67 and 0.60 g/fry and 32.0 and 31.3 mm/fry total length for the control and MT treatments, respectively. The mean final individual weight and length for blue tilapia were 0.36 and 0.34 g/fry, and 25.9 and 27.5 mm/fry for the control and MT treatments, respectively. Fry survival for the control and MT treatments averaged 66 and 84%, and 96 and 91% for Nile and blue tilapia, respectively.

Progeny Testing to Identify "YY" Male Tilapia

Ronald P. Phelps
Department of Fisheries and Allied Aquacultures
Auburn University, Alabama, USA

Abstract

Males from nine populations possibly containing males of a "YY" genotype were mated with normal females. The sex ratios of the offspring of 4 of the 49 matings examined in FY 94 suggest that four YY males were identified. Two males which produced > 95% male progeny in the first mating did not consistently produce high frequencies of males in later spawns. These results suggest that sex inheritance is not strictly a male-determined characteristic and increases the difficulty of breeding a form of Oreochromis niloticus that will consistently produce all-male progeny.

Bioconversion of Gastropods by Black Carp in Egyptian Fish Culture Ponds

Work Plan 7, Study 2B

William L. Shelton
Zoology Department
University of Oklahoma
Norman, Oklahoma, USA

Kevin D. Hopkins
College of Agriculture
University of Hawaii at Hilo
Hilo, Hawaii, USA

Ashraf Soliman and Abdel L. El Gamal
Central Laboratory for Aquaculture Research
Agricultural Research Center
Abbassa, Egypt

Abstract

Bioconversion research focuses on the transformation of an underutilized resource into fish flesh, while simultaneously resolving or reducing a management problem. Snails are abundant in Egyptian aquatic systems; several species are also significantly related to human health problems. An experiment was conducted to evaluate the use of black carp (Mylopharyngodon piceus) as a biological control of snails. Ponds were prepared by hand cutting aquatic plants to near the soil surface in March/April. Supply problems delayed stocking which commenced in June. All ponds were contaminated with wild (unstocked) fish which is believed to have influenced the growth rate of black carp. Black carp grew least in ponds that were contaminated by common carp and mullet. Data analysis continues.

Bioconversion of Nuisance Aquatic Plants by Grass Carp in Egyptian Fish Culture Ponds

Work Plan 7, Study 2A

William L. Shelton
Zoology Department
University of Oklahoma
Norman, Oklahoma, USA

Kevin D. Hopkins
College of Agriculture
University of Hawaii at Hilo
Hilo, Hawaii, USA

Abdel R. Mostafa and Abdel L. El Gamal
Central Laboratory for Aquaculture Research
Agricultural Research Center
Abbassa, Egypt

Abstract

Aquatic weeds are a management problem in Egyptian aquaculture. They also represent an underutilized resource. Grass carp, Ctenopharyngodon idella, is known to feed on several aquatic plants. An experiment was carried out to determine if grass carp could be used as a biological control of nuisance weeds in Egyptian pond aquaculture. Ponds were prepared in March/April. Macrophytes, primarily Typha and/or Phragmites were hand cut to near the soil surface. Ponds were refilled and the area of plant development was estimated visually by predominant species. Supply problems necessitated a delay of grass carp stocking, so that some plant regrowth had occurred. Initial data indicate that grass carp were effective in maintaining ponds virtually free of emergent vegetative regrowth. However, because of the delayed stocking grass carp were not able to completely control Azolla and Certophyllum. In several ponds these plants were able to develop and reach greater than 40% coverage.

Interaction of Grass Carp and Black Carp in Egyptian Fish Culture

Work Plan 7, Egypt Study 2C1

William L. Shelton
Zoology Department
University of Oklahoma
Norman, Oklahoma, USA

Kevin D. Hopkins
College of Agriculturev
University of Hawaii at Hilo
Hilo, Hawaii, USA

Ashraf Soliman and Abdel R. El Gamal
Central Laboratory for Aquaculture Research
Agricultural Research Center
Abbassa, Egypt

Abstract

Bioconversion of plants by grass carp and of snails by black carp can be considered as separate components in a polyculture system, but they are also interrelated because the plants provide food an cover to snails and thus affect black carp predation. Gastropod production might diminish by virtue of grass carp feeding on plants, but is unclear to what extent the predation of black carp on snails is influenced by grass carp feeding. Abundant vegetation could provide protection for snails, so that their biomass might increase in the presence of black carp rather than being suppressed by predation. A study was conducted to investigate these relationships. Data are being analyzed.