Genetics of Body Color in Tilapia mossambica

Gold, bronze, and black (normal pigmentation) body colors in Tilapia mossambica are controlled by a single autosomal gene with incomplete dominant gene action: GG fish are black gg fish are gold; Gg fish are bronze. Because gold body color is produced by the recessive genotype, it is easy to produce and to maintain a truebreeding population of gold T. mossambica for commercial purposes. If all other colors are culled, the population will breed true, because gold × gold will always produce 100% gold offspring. The G gene will be a valuable genetic marker for many genetic studies, such as the production of gynogenetic T. mossambica .     

Effects of Intraspecific Hybridization in Tilapia nilotica on Survival Under Ambient Winter Temperature in Alabama

Viability under ambient winter temperatures in Alabama was assessed for Auburn University-Egypt and Auburn University-Ivory Coast strains of Tilapia nilotica and their F₁, F₂, and four backcross hybrids. Egypt strain was more viable ( P = 0.05) than Ivory Coast strain. Observed mean viabilities of the F₁ hybrids were intermediate between those of the parental strains. Viabilities of the reciprocal F₁ hybrids were not significantly different. Viabilities of the reciprocal F₂ hybrids were not significantly different. Backcross hybrids that were produced by crossing F₁ hybrid females to Egypt strain had a greater observed mean viability than those that were produced by crossing F₁ hybrid females to Ivory Coast strain. Average viabilities of the parental strains, F₁, F₂, and backcross hybrids were not significantly different. Heterosis in F₁, F₂, and backcross hybrids was −1.39%,−0.82%, and −2.08%, respectively. Viability under ambient winter temperatures in Alabama in T. nilotica appears to be controlled by additive rather than by dominance effects, which means that selection rather than crossbreeding is the breeding technique that should be evaluated to improve this trait in T. nilotica .     

Food habits and growth of silver and bighead carp in cages and ponds

Analysis of intestinal contents of silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) showed that silver carp consumed primarily phytoplankton while bighead carp consumed large quantities of zooplankton and detritus in addition to phytoplankton. The size of particles filtered by the bighead carp was larger (17–3,000 μm) than that filtered by silver carp (8–100 μm). Artificial feed was readily consumed by bighead carp but not by silver carp. No growth difference was indicated for silver carp in fertilized ponds and ponds receiving artificial feed. Growth of bighead carp increased substantially with the addition of artificial feed. Silver carp grew more rapidly in cages than bighead carp.     

The Economics of Intensifying Catfish Production: A Production Function Analysis1

Yields of channel catfish in the United States have increased as a result of higher levels of stocking, feeding and aeration. A Cobb-Douglas production function was estimated using survey data from 66 catfish ponds in West-Central Alabama to determine if further intensification of catfish production in West-Central Alabama would be profitable. Feed, capital, stocking rate, and length of production period explained most of the variation in yield. Values of the marginal products for feed, stocking rate and capital were consistently higher than input costs during the study period. Profit-maximizing levels of input use were higher than the levels of inputs used in West-Central Alabama during the study period. Results indicated that more intensive use of production inputs would increase yield and profits. However, careful interpretation of these results requires consideration of non-profit factors such ns cash Row and risk as well as the specific nature of the data used to develop the production relationship. The method utilized in this study can generally be applied to any aquaculture production system, but the recommendation for more intensive input use is specific to the pond data collected for this study.     

Estimates of Additive Genetic Effects, Maternal Genetic Effects, Individual Heterosis, Maternal Heterosis, and Egg Cytoplasmic Effects for Growth in Tilapia nilotica

Lengths and weights of Auburn University-Egypt and Auburn University-Ivory Coast strains of Tilapia nilotica and their F₁ F₂, and backcross hybrids were analyzed by multiple regression to estimate strain additive genetic effects, strain maternal genetic effects, individual heterosis (specific combining ability), maternal heterosis, and strain egg cytoplasmic effects for growth to determine why heterosis of the F₂ and backcross hybrids was greater than that of the F_I hybrids. Individual heterosis and maternal heterosis made the greatest contributions to growth. The F₂ and backcross hybrids were larger than the F₁ hybrids because of maternal heterosis. Regression coefficients were used to predict growth for any possible hybrid combination. Egypt ♀× Ivory Coast ♂ F_I hybrid females backcrossed to Egypt males and Egypt ♀× Ivory Coast ♂ F₂ hybrids were the largest groups evaluated in this study and were also predicted to have faster growth rates than any other possible Egypt-Ivory Coast hybrid.     

Relative growth,survival and harvestability of bighead carp,silver carp,and their reciprocal hybrids

Growth and survival in the primary rearing phase (42 days) for bighead carp, silver carp, bighead × silver carp (BHC × SC), and silver × bighead carp (SC × BHC) in ponds and concrete tanks stocked at 370 500 fry/ha were studied. Mean survival for fishes in ponds was 93%, that in tanks was 73%. Yields among all fishes averaged 338 kg/ha. The growth rates of fishes in ponds were similar; in tanks, silver carp grew faster than the bighead carp.Growth, survival, and harvestability by seine during the secondary rearing phase (60-day duration) for the same groups of fish were studied. Fingerlings (0.9 g mean weight) were stocked in earthen ponds at 49 400 fish/ha and 98 800 fish/ha. Mean survival of fishes at low stocking rate was 77%, similar to that (71%) for the high stocking rate. Fish yields were similar at the low stocking rate. At the high rate, the BHC × SC yield (846 kg/ha) was greater than the SC × BHC yield (582 kg/ha). The BHC × SC and SC × BHC had greater mean weights at low stocking rate than at high stocking rate. The mean weights for bighead carp were similar at both rates. Bighead carp and the reciprocal hybrids were more easily harvested by seine than silver carp.