The nursery culture and nutrition of post-larval black tiger shrimp Penaeus monodon Fabricius

Abstract

An evaluation was made of the role of secondary nursery rearing within the intensive shrimp culture industry. A series of concrete nursery tank trials were conducted rearing post-larval Penaeus monodon Fabricius for 35 days from PL,5 to PL50. Shrimp production was directly related to stocking density at up to 2,000 shrimp m'^ but growth, survival, FCE and size range were negatively density dependant. Water exchange and aeration were necessary to maintain shrimp production at high density. The use of mesh habitats and sand substrates and the effects of dietary formulation and feeding regime also influenced shrimp production. The production of shrimp nursed in net cages was comparable to that of shrimp nursed in concrete tanks at densities of 500 shrimp m'^. An economic analysis of secondary nursing in tanks suggested that it may be profitable if the value of the juvenile shrimp produced is > 2.5 times that of postlarvae. A cage on-growing trial showed that the stunting of shrimp during high density secondary nursing was not permanent, but was rapidly compensated for by increased growth rate during on-growing at lower density. A stress test was developed which enabled quantification of the stress tolerance (vigour) of post-larval shrimp. This entailed direct transfer of post-larvae into water at reduced or increased temperature and salinity for one hour. The tests facilitated discrimination between batches of post-larvae produced from a single hatchery. The stress resistance of juvenile shrimp following secondary nursing was significantly better than that of exhatchery post-larvae, suggesting that older or secondary-nursed juveniles are more likely to survive transfer and subsequent on-growing than are primary-nursed post-larvae. Low vigour shrimp are suggested to have poor growth potential, although further research into the effects of shrimp vigour on shrimp production during pond on-growing is required. A series of nutritional trials were conducted in laboratory and outdoor nursery tanks to study the optimal levels of, and relationship between, protein, lipid, carbohydrate and energy in diets for post-larval P. monodon. Lipids including cod liver oil:soybean oil (3:1), soy lecithin (3-6 %) and cholesterol (0.5 %) were necessary to optimise shrimp production. Dietary lipid levels of 8-12 % in nutrient balanced diets maximised shrimp survival and production. Carbohydrate (starch) levels of 21-38 % were optimal in nutrient balanced diets at carbohydrate:lipid ratios of 2-5:1. Both carbohydrate and lipid were shown to be able to spare protein for growth. Protein levels were decreased from 44 % to 38 % in nutrient balanced diets without compromising shrimp production. Further reductions in protein levels may be possible in nutrient balanced diets. The level of protein supporting-optimal shrimp production was shown to be directly related to the total energy and protein:energy ratio of the diet. Models are proposed for estimating the level and proportions of protein, lipid and carbohydrate which are best able to supply the nutrient and energy requirements of post-larval P. monodon. The benefits of reducing the protein level of shrimp diets are discussed in terms of minimising diet cost and feed wastage