A novel two-step procedure for mass production of all-male populations of the giant freshwater prawn Macrobrachium rosenbergii

Males of the giant freshwater prawn Macrobrachium rosenbergii grow faster and reach higher weights at harvest than females a fact which makes the culture of all-male populations desirable. All-male populations were produced by mating sex-reversed males, i.e., neofemales, with normal males. Neofemales capable of mating and spawning were produced by removal of the androgenic gland (AG) from immature M. rosenbergii males. The main obstacle to developing a technology based on this type of manipulation is the difficulty of identifying males at a sufficiently early stage of development. To overcome this problem, we developed a novel two-step scheme for large-scale microsurgical andrectomy. Phase I post larvae were andrectomized at ages 25–60 days after metamorphosis (PL25–60). A low success rate of functional sex reversal, resulting with all male progeny was obtained (1.3%). In the light of the low success rate and a number of cases of abnormal reproductive development, a second phase was introduced in which the progeny (presumed males) of neofemales from phase I were andrectomized at earlier ages (PL20–30). This two-phase protocol enabled a large quantity of juvenile males to be andrectomized. In phase II there was a significant increase in the number of sex-reversed animals (developed ovaries) and a significant shortening of the time to maturation. Comparison of the all-male progeny with a normal mixed population showed higher growth performance of the all-male population. This advantage together with the shorter maturation time in phase II opens the possibility to scale-up the system to field conditions. Since sexual dimorphic growth patterns are common among decapod crustaceans, it is obvious that the results of this study will have applied significance for many aquacultured species.