Neo-females production and all-male progeny of a cross between two Indian strains of prawn (Macrobrachium rosenbergii): Population structure and growth performance under different harvest strategies

Culturing all-male giant freshwater prawn (Macrobrachium rosenbergii) presents a promising avenue for increasing yield and income. A sex reversal technology through androgenic gland (AG) manipulation was introduced, posing an increased risk of inbreeding. Thus, a scheme for Kerala (K) and West Bengal (WB) strains crossing using neo-females from one strain with males from the other strain was suggested.Microsurgical sex reversal was applied in juvenile males of the Kerala strain at developmental stages of PL₁₅, PL₃₀, PL₄₅ and PL₆₀. Improved success rates of feminization were achieved when the intervention was performed at early developmental stages. Prawns operated at the PL₁₅ and PL₃₀ stages began developing ovaries as early as 105days after metamorphosis and were able to produce offspring. A grow-out experiment in earthen ponds of all-male progeny originating from Kerala neo-female×West Bengal males was performed and the effect of selective harvest (SH) of <50g prawns was compared to a final harvest (FH) strategy. The survival rate in the SH group was significantly higher than that in the FH group. Specific growth rate was significantly lower in the FH than in the SH group, while the feed conversion ratio was significantly lower in the SH than in the FH group. Distribution of fast-growing orange clawed (OC) males in the SH group was substantially narrower, peaking at 55-60g, while in the FH group OC males were distributed over the size range of 30-150g, suggesting further growth potential. Moreover, the terminally molted Blue Clawed (BC) males presented only small portion of the males; 7% and 0.7% in the FH and SH groups, respectively. The frequency of the large male (>100g) marketable size group was significantly higher, and that of the medium-sized (5075g) group was lower in the FH treatment in comparison with the SH.The cross tested herein demonstrated substantially higher yield than that obtained in previous studies, however, no statistically significant difference in net productions was found between the FH and SH treatments (2207±130 versus 2163±137kgha^-1, respectively). Cost-benefit analysis after nine months of grow-out showed higher profit and higher benefit-cost ratio in the FH group. However, the SH treatment resulted in more uniform marketable prawns and suggested a continuous cash flow throughout the grow-out period.