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An 8-week feeding trial was conducted to evaluate the effects of dietary γ-aminobutyric acid (GABA) on growth performance, immune response, and disease resistance for juvenile whiteleg shrimp, Litopenaeus vannamei. Five isonitrogenous diets were formulated by supplementing 0 (CON), 50 (GABA50), 100 (GABA100), and 300 (GABA300) mg of GABA and 4 g of oxytetracycline (OTC) per kilogram of diet. A total of 225 juvenile whiteleg shrimp with an initial weight of 2.97 ± 0.06  g were randomly distributed and reared in 15 aquaria as triplicates. After 8 weeks of the feeding trial, weight gain, specific growth rate, feed efficiency, and protein efficiency ratio of shrimp fed GABA100 were significantly higher than those of shrimp fed CON, GABA50, and GABA300 diets ( P < 0.05 ). However, there were no significant differences among shrimp fed CON, GABA50, GABA300, and OTC diets ( P > 0.05 ). After nine days of challenge test with Vibrio alginolyticus, the average cumulative survival rate of shrimp fed GABA50, GABA100, and OTC was significantly higher than that of shrimp fed GABA300 and CON diets ( P < 0.05 ). These results may suggest that 100 mg dietary GABA supplementation (including endogenous GABA, 175.6 mg/kg diet) per kilogram of diet could be the optimum dietary level to replace antibiotics and improve growth performance and disease resistance in whiteleg shrimp L. vannamei.

Shrimp farming is a key component of Vietnamese aquaculture contributing ~5% to their gross domestic product annually. Environmental hazards and socio‐economic parameters among other factors influence shrimp productivity in Vietnam. The present study employed the stochastic frontier production approach to investigate how technical efficiency (TE) of semi‐intensive and intensive shrimp farms is influenced by socio‐economic factors and environmental hazards. A questionnaire was administered to ascertain farmers' cost of major inputs (labour, seed, feed and lime), socio‐economic factors, coupled with environmental hazards (flood, pollution and drought experience). Findings revealed a mean TE of approximately 65% and 76% for semi‐intensive and intensive farms respectively (though, non‐significant as p ≥ 0.05). The input variables, shrimp seeds, feed and lime were found to be important variables in the intensive systems, as they positively correlated with TE in intensive systems. In the inefficiency model, education positively correlated with the TE in both systems, indicating that educated farmers are more efficient. Pollution negatively correlated with TE in both systems. With <80% of the farmers extremely affected by floods and droughts, and about 95% affected by pollution, the present study concludes there is a thorough impact of the above environmental hazards on farmers' technical efficiency.

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The food and feeding habits of eight (8) fish species Elops lacerta, Chrysichthys auratus, Schilbe mys-tus, Sardinella maderensis, Synodontis schall, Hepsetus odoe, Tilapia zillii and Mugil cephalus in Ogun estuary, Ogun State, Nigeria were studied and estimated for six months, between February and July, 2014. A total of 470 fishes were randomly collected from the commercial fishermen during the study. Results from the stomach contents analysed using frequency of occurrence and numerical methods showed that S. mystus, E. lacerta, S. maderensis, H. odoe, S. schall, T. zillii, M. cephalus and C. auratus were predators, piscivores, herbivores, piscivores, omnivores, herbivores, herbivores and omnivores respectively while H. odoe and S.mystus partly fed on E. lacerta and T. zillii respec-tively. The Diet Breadth (D) ranged from 0.76 to 0.88 and the percentage Gut Repletion Index (GRI), a reflection of frequency of feeding, ranged between 60-100%.