Production of all-male stock by neofemale technology of the Thai strain of freshwater prawn, Macrobrachium rosenbergii

The giant freshwater prawn, Macrobrachium rosenbergii is commercially cultured in many tropical countries. Males of this species grow much faster than females so that, obviously, culture of an all-male population produces significantly higher yield than an all-female or mixed-sex culture. Although sex of M. rosenbergii is determined by genetics, sex reversal from males to females can be triggered by the removal of androgenic glands at an early stage. The empirical information obtained from two families showed that almost all offsprings of the neofemales were male. Therefore we conducted this study to explore the result of such mating with sufficient number of crosses in the Thai strain of M. rosenbergii. The histology of the gonads during the threshold period of sex determination was also studied. The results showed that the gonadal differentiation of M. rosenbergii did not occur until the stage that both gonopore complexes and appendix masculinae appeared in males. The bilateral removal of androgenic glands of a total of 87 postlarvae at stage I (presence of the gonopore complexes but not the appendix masculinae) resulted in 80.4% survival. Among the survivors 30% developed as female and 27.14% eventually matured. Mating of 12 neofemales with normal males resulted in all-male offspring in eight crosses; 88–99.49% males in two crosses. The remaining two crosses produced offspring with 1:1 sex ratio and hence were attributed to mislabeling of the normal female as neofemales. The 10 control crosses (normal male × normal female) produced varying offspring sex ratios from 1:1 (six crosses) to 1.72♀:1♂ (pooled data from four crosses). Fecundity of the neofemales was not different from that of the normal females. Our results suggest that the application of the neofemale technology to produce all-male stock for aquaculture is promising.