Broodstock and larval nutrition
From experience in aquaculture most farmers now recognize that broodstock development including nutrition are important, not only from the point of view of the reproductive success of the stock, but also for obtaining healthy larvae and fry to ensure the health of the off-spring and the hatchability and survival of the larvae. It has been shown that essential fatty acids, vitamins A, E and C, trace minerals, b-carotene and other carotenoids can affect fecundity and egg quality (De Silva and Anderson, 1995) and that the amino acid requirements of broodstock are probably similar to those for optimal growth (De Silva and Anderson, 1995). Studies indicate that there is great species diversity in nutritional requirements and their effect on reproduction.
Hasan (2001) has pointed out that the nutrition of male broodstock for the improvement of sperm quality through dietary manipulation has not so far been investigated.
In studies made for a period of eight months prior to spawning, Watanabe et al. (1984) found that EFA (n-3 PUFA) deficient diets in red sea-bream produced eggs with significantly lower survival rates and high levels of larval deformity. Nutritional requirements can differ according to the reproductive phase. These phases may be considered as from commercial size to broodstock size, immediately prior to or during spawning, and post-spawning. Thus the formulation of broodstock diet specific to the reproductive stages/periods concerned, should take into consideration the optimised grow-out diet to meet the full nutritional requirement of the species from commercial to broodstock size and subsequent reproductive stages.
The transition from an endogenous (yolk sac and oil globules) to an exogenous food supply, which marks the onset of the larval stage, is the most critical phase of the life cycle when much of the mortality of hatchery-reared stock takes place. Absolute nutrient requirements during this phase of aquatic animals is little known, even though it is generally acknowledged that the feeding of larvae has a dominant role in larval survival. There are species that will feed on artificial diets,but it is supplemented with live zooplakton and phytoplankton to satisfy all nutritional requirements. Some species require microparticulate diets in addition to live foods (Kanazawa, 1991). Live foods constitute the main diet of marine fish larvae, but a single live food is often unable to satisfy the nutrional requirement of the species under culture. Many studies have been conducted on the effect on organisms of various nutrients. The indications are that larval fish require a diet with high protein content and sufficient amounts of essential fatty acids (Lavens et al.,1991).The live feeds that have been investigated are brine shrimp (Artemia spp.) and rotifer (Brachionus plicatilis). Methods of bioencapsulation have beendeveloped to incorporate particulate products into brine shrimp nauplii to improve its content of essential fatty acid. The nutritive value of rotifers is improved by culturing them in a suitable medium such as w-yeast and by feeding with a mixture of homogenized lipids and baker’s yeast or marine alga (Chlorella spp.).The specific fatty acids required vary between species (De Silva and Anderson, 1995). The nutrient quality of live food is not achieved when larvae are reared in natural pond conditions under semi-intensive farming systems, where planktonic growth is stimulated by fertilization, to natural productivity as in the case of rearing carps.
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