Mark W. Rosegrant

Economic assessment and policy recommendations of fisheries development strategies in Vanuatu

The freshwater prawn, Macrobrachium rosenbergii is a more popular crustacean cultured widely in monoculture system in India. It has got high nutritional value in the human diet. Hence, understanding its enzymatic and body composition is important in order to judge its flesh quality. Fish oil specially derived from Indian oil sardine is a good source of highly unsaturated fatty acid and lipid source in fish/prawn diet. A 35% crude protein diet with graded levels of Sardine oil as a source of fat was incorporated at four levels viz, 2.07, 4.07, 6.07 and 8.07% maintaining a total lipid level of feed at 8.11, 10.24, 12.28 and 14.33% respectively. Diet without sardine oil (6.05% total lipid) was served as basal treatment. The giant freshwater prawn, Macrobrachium rosenbergii was used as test animal and the experiment was lost for 112 days. Significantly higher gain in weight of prawn was recorded in the treatment with 6.07% sardine oil incorporation followed by higher specific growth rate, food conversion rate and protein efficiency ratio. The 8.07% sardine oil diet produced the highest RNA: DNA ratio in the prawn muscle. Digestive enzyme analyses in the digestive tract and midgut gland showed the greatest activity in prawns fed the 8.07% diet.S of the Background: Macrobrachium rosenbergii is one of the most important prawns in freshwater aquaculture. Male giant freshwater prawns grow faster and reach higher weights at harvest than females, which make the culture of all-male populations desirable. The purpose of this study is to explore the molecular information of new gene and its potential physiological function on sex regulation. Methodology & Theoretical Orientation: The gene expression pattern was studied using Real-time RT-PCR. The functional role of gene in vivo by RNA interference (RNAi) was utilized and its effect on sex regulation was evaluated. Findings: In this study, a novel gene of the full-length cDNA encoding a masculinizing factor from the giant freshwater prawn Macrobrachium rosenbergii was termed Mr-Masc. Real-time RT-PCR analysis revealed that Mr-Masc gene expression was obviously difference between male and female prawn, and dominantly expressed in the ovary of the reproductive tract in female prawn. To elucidate the functional role of Mr-Masc in vivo, the Mr-Masc gene was disrupted by RNA interference (RNAi). In vivo silencing of the gene, by injecting the all-male and monosex postlarvae with Mr-Masc double-stranded RNA, sex-revsersed females (neofemales) were obtained. Moreover, all-male progeny was produced by mating neofemales with normal males and these all-male populations showed good growth potential and market value in the aquaculture. Conclusion & Significance: It was firstly reported the full and functional sex reversal of male freshwater prawns through the silencing of a single Mr-Masc encoding gene. Neofemales capable of mating and spawning were produced by the RNAi technology at a sufficiently early stage of larval development. This finding offered an insight regarding the biology and evolution of sex differentiation regulation. 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 aqua cultured species.