Inert feeds

Artemia, especially when enriched, have become the standard food for successful hatchery culture of freshwater prawn larvae (Devresse et al. 1990; Merchie et al. 1995b; Romdhane et al. 1995). However, interest continues with the development of formulated feeds that will better supplement or completely substitute this live food during the larval production phase. The main incentives for this effort are the high cost and uncertain supply of cysts, the need for extra infrastructure to hatch the cysts and enrich the larvae, and the potential for introducing pathogens into the culture tanks.

Early efforts in M. rosenbergii larviculture involved the addition of fish flesh as a commonly used feed supplement for Artemia in Hawaii, Asia and South America (Malecha 1983; New & Singholka 1985; Valenti 1985). More recently, hatcheries have used an improved variation of this farmmade feed. Minamizawa & Morizane (1970) and Murai & Andrews (1978) successfully supplemented newly hatched brine shrimp with chopped fish and short-necked clam, and freeze-dried oyster meat, respectively. New (2002) recommended alternative farm-made larval feeds that included a range of ingredients, including mussel flesh and skimmed milk as well as fish flesh and fish meal (see also section Efforts by Daniels etal. (1992), Valenti etal. (1998) and Pitipornchai (1998) have confirmed the validity of this strategy by showing that Artemia nauplii alone do not provide all of the nutritional requirements of M. rosenbergii for late-stage larval growth. This is true of n-3 fatty acids, notably DHA (22:6 n-3). The nutritional deficiency of Artemia was also illustrated in the results of the study conducted by Nair et al. (2007) who found that supplementing 50% Artemia with 50% of a commercially available, freeze dried product consisting of an arctic lake copepod rich with PU-FAs and astaxanthin (Cyclop-eeze®) was effective. Use of this product yielded survival to metamorphosis that was significantly greater than that of larvae fed a control diet of Artemia and egg custard alone. In addition, the practice of supplementing Artemia has been shown to improve the survival and metamorphosis of prawn larvae (Pitipornchai 1998). These findings support the supplementation use of Artemia with an inert feed. Though widely accepted, these natural-product based supplemental feeds have a number of drawbacks that limit their use in intensive hatchery systems, for example highly variable size of the particles; variability in nutrient quality and composition; high leaching rates;

potential bacterial contamination; and an inherent detrimental influence on culture water quality. As a result, focus has turned to production of more uniform, formulated (artificial) diets, which do not have these inherent negative characteristics.

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