Author(s): Chamberlain GW
A major impediment to shrimp farming is the lack of reliable technology for reproducing shrimp in captivity. The objective of this research was to develop and evaluate nutritional and environmental strategies for inducing captive shrimp to mature andspawn. The approach was to assess gonadal maturation in wild populations of shrimp and to use this information as a guide in attempts to manipulate reproduction in the laboratory. In the evaluation of wild populations, Penaeus setiferus and P. aztecus were collected throughout the year at 27 stations in the Gulf of Mexico to examine temporal, spatial, and size-related variations in reproductive activity. Biochemical analyses of the gonad and hepatopancreas of approximately 3,000 shrimp indicated that both species probably depend on current food intake for most of the nutrients required for vitellogenesis. Laboratory experiments implemented hormonal, nutritional, and environmental treatments in a stepwise fashion, with each new experiment incorporating the best performing levels of treatments evaluated previously. The first experiment indicated that a composite diet consisting of squid, polychaete worms, clams, and shrimp yielded greater growth, molting rate, maturation, and ovary size of P. vannamei than any of these foods singly. The second experiment, which utilized the composite diet of the first study, determined that light intensity differentially affected number of spawns of P. vannamei and P. stylirostris, and that unilateral eyestalk ablationstimulated both male and female gonadal maturation. The third experiment induced spawning of P. stylirostris from Mexico, Costa Rica, and Ecuador using a composite diet, dim light intensity (indicated by the second study), and eyestalk ablation of females. Results indicated: (1) a decline in spawning frequency of females 60-75 days after ablation; (2) diminished numbers of eggs and rates of hatching and metamorphosis after repeated spawning; (3) increasing fecundity and decreasing naupliar metamorphosiswith increasing female size; and (4) higher fecundity of the Mexican stock than either the Costa Rican or Ecuadorian stocks. The final two experiments induced maturation of unablated P. setiferus and P. stylirostris using pelleted diets, dim light intensity, and temperature and photoperiod manipulation. Dietary supplementation with tocopherol did not prevent the recurring Male Gonadal Degeneration Disease, but it did improve percentage of normal sperm, rate of ovarian maturation, and frozen storage stability of shrimp tail muscle.