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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.
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.
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. 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. 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 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. 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. 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. The Pond Dynamics/Aquaculture CRSP is funded under USAID Grant No. LAG-G-00-96-90015-00
and by
the participating US and Host Country institutions.
Questions for or about the Aquaculture CRSP? Comments about this site? Email ACRSP@oregonstate.edu.
Effects of Form of Defatted Rice Bran Offered on Nile Tilapia Production in Ponds
Abstract
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
Abstract
Use of 17a-Methyltestosterone for Tilapia Sex Reversal
Work Plan 7, Egypt Study 4A2
Abstract
Progeny Testing to Identify "YY" Male Tilapia
Abstract
Bioconversion of Gastropods by Black Carp in Egyptian Fish Culture Ponds
Work Plan 7, Study 2B
Abstract
Bioconversion of Nuisance Aquatic Plants by Grass Carp in Egyptian Fish Culture Ponds
Work Plan 7, Study 2A
Abstract
Interaction of Grass Carp and Black Carp in Egyptian Fish Culture
Work Plan 7, Egypt Study 2C1
Abstract
Disclaimers
