| Experiments were conducted to evaluate different procedures to control gender differentiation and the expression of male morphotypes in the freshwater prawn, Macrobrachium rosenbergii. Dietary administration of 17α-methyltestosterone (MT) at concentrations of 100, 200, and 400 mg/kg of diet fed for 20, 40, and 60 days did not alter the percentage of the population which was male. Dietary administration of dopamine to recently metamorphosed postlarvae for 60 days at concentrations of 0.15, 1.5, and 15.0 mg/kg significantly increased the percentage of individuals without external male characteristics. This is the first reported use of dietary administration of dopamine to crustaceans and the first evidence that development of gonads and possibly gender differentiation of crustaceans are affected by dietary administration of any compound. Histology was conducted on samples of prawns fed diets containing MT, dopamine, and those provided neither compound. Gonadal tissue was identified in 72% of prawns submitted to histological analysis but could only be confirmed as ovaries or testes in 8%. Loss of MT from diet was determined after submersion in water for 0, 15, 30, 60, 90, 180, and 360 minutes. Mean MT loss from diets submersed in water ranged from 2.3 to 15.4% for all time periods. No appreciable differences in loss of MT were observed between different size diets, or whether MT was added to diets through alcohol evaporation or included as part of a dietary oil ingredient in the formulation. Successful in vitro incubation of eggs of M. rosenbergii to hatch was not realized when incubation was initiated 1–3 days post-fertilization. Fouling occurred when egg masses were incubated in vitro, but was minimized by incubating single eggs and adding formalin to the incubation system. Numerous compounds and enzymes, alone and in combination, were evaluated as means to breakup egg masses into single eggs while maintaining their viability. A 20 minute exposure to 0.4 ppm of a 5.25% hypochlorite solution or a combination of 0.6% papain and 1.5% sodium sulfite, was most effective and egg viability appeared to be maintained. |
