Preliminary study on production of Neofemale brood stock of Giant freshwater prawn, Macrobrachium rosenbergii in Hatchery

Productivity of giant freshwater prawn is generally associated with the brood stock management and it can be improved by two methods: selective breeding and all male culture. Few studies have indicated economically advantages of all male culture. However, conventional methods by manual sexing and selecting the male prawn during grow-out is time and labour consuming.  Another method to produce male fry is to use 'neo female' parent. This study was conducted to produce the 'neo female' brood stocks and evaluate the empirical percentages of success rate in the hatchery. A batch of 20,000 post larvae were nursed in a 40 tonnes rounded concrete tank. At day 45 of nursing, first segregation to identify male PLs was carried out by checking the presence of a pair of 'genophore complexes' located at the edge of fifth walking leg. Out of 2,000 PLs, only 600 were males (representing 30% of the population). These males were subsequently undergoing 'androgenic gland ablation' by removing the a pair of glands in a minor surgery.  After a week of the removal procedure, 87.7 ± 3.0% of the males survived. After a month, the survived males were examined to check the presence of 'appendix masculine' (male organ structure). It was found that 84.7 ± 3.5% of the candidates were successfully reverse to female as their 'genophore complexes' and 'appendix masculine' were absence. They were raised in tanks for six to eight months until maturity. Mating of these 'neo female' brood stocks with normal males at a ratio of 4 to 1 have produced 50.3 ± 3.5 % berried stocks. Relative fecundity of the 'neo female' is comparable to the normal brood stock ranging from 408 - 1080 larvae/g brood stock. Result also showed that the success rate of producing the neo female was 22.3 ± 2.6%.

Keywords: Neo female, sex reversal, all male, brood stock, giant freshwater prawn