Info

* Adisukresno etal. (1982).

** Tunsutapanich etal. (1984); Pitipornchai (1998).

feed which is preferred by the prawn larvae (A. Tunsutapanich, pers. comm. 1999). Fish, crab, squid and mollusc meat, which are ground and sieved to a particle size of 300 to 500 p.m, are sometimes added to these egg custards. The cooked custard is broken up into small particles through a series of fine sieves, according to the size of larvae. In practice this farm-made feed is freshly prepared every 2 days (Tunsutapanich et al. 1984; Pitipornchai 1998). The egg custard is administered during daytime only, during which time the quantity of Artemia nauplii gradually declines until the evening, when new nauplii are added. In Thailand, after metamorphosis occurs, the PL are normally fed with a 100% custard diet, of which a portion of the eggs is substituted by fish, crab, squid and/or mollusc meats previously ground and sieved to a size of 300 to 500 p.m.

Corbin etal. (1983) and New (2002) recommended that inert feed particles of about 0.3 mm should be used up to rearing day 10 to 12; from then until metamorphosis, particles that gradually increased to 1.0 mm were suitable. Sick & Millikin (1983) reported that porous, pliable gels cut into 3 mm cubes were readily acceptable to all larval sizes. In Brazil, the optimal range of feed particles for different larval stages are stated to be 0.2 to 0.4, 0.4 to 0.7 and 0.7 to 1.0 mm for larval stages IV to VI, VII to VIII and IX to PL, respectively (Correia & Castro 1998). The graded particles are then collected and stored in a refrigerator. A study comparing feed intake and acceptance ofboth dry and wet formulated feeds (Barros & Valenti 2003a) found no significant differences between the size of the inert diet and the food intake frequency. The amount of feed consumed, measured by microscopic examination of the gut, was not dependent on food size. Prawn larvae during stages VII to XI fed equally well on Artemia and a wet diet, suggesting that larvae could be fed nauplii to stage VI, followed by a shift to inert diets from stage VII onwards.

Nair & Hameed (1992) described the use of a coagulated suspension of 1 kg of'thelly (Metapenaeus dobsonii) meat mixed with 10 hens eggs in commercial freshwater prawn larviculture in India. After blending and coagulation by gentle cooking, this feed was sieved to produce 200 to 400 p.m particles for larval stages up to IV, 400 to 600 p.m for stages V to VIII and 600 to 1000 p.m for stages IX to XI. This feed was supplied with a daily (evening) supply of Artemia at 3 to 5 nauplii/ml. Alam et al. (1995b) describe an egg custard enriched with cod liver oil, which was used in conjunction with Moina micrura for feeding freshwater prawn larvae.

Lipid and fatty acid nutrition continue to be a focus in improving the efficacy of inert diet formulations. In comparing growth and fatty acid composition of M. rosenbergii larvae, Kamarudin & Roustaian (2002) examined the replacement of cod liver oil with corn oil in different proportions. The larval fatty acid profile reflected that of the diet and while PUFAs were dominated by n-3 fatty acids, the ratio of n-3 to n-6 fatty acids remained stable among treatments, suggesting the importance of specific fatty acid requirements by larvae. No evidence of de-novo synthesis of linoleic acid was apparent. However, the higher percentage of arachidonic acid found in larval tissue compared to that test of diets and Artemia, suggest the ability of larvae to synthesise this fatty acid by elongation and desaturation of linoleic acid. In a comparison of egg-custard diets containing various ratios of squid oil (SO) to soybean oil (SBO) and lecithin, Hein et al. (2005) reported that SO treatments resulted in the greatest total body length and survival. This was likely to be due to the higher concentration of n-3 HUFAs, especially EPA (20:5 n-3) and DHA (22:6 n-3) contained in the SO, which was also reflected in the fatty acid composition of the PL as compared to less n-3 HUFAs present in PL fed the SBO diet. Supplemental lecithin was shown to improve survival and metamorphosis, though not weight gain. These results contrast with earlier findings with juveniles that did not show increased survival, and may indicate that phospholipid requirements are age-dependent. The findings ofthis study illustrates that a diet containing 3% SO and 1.5% lecithin would be useful. The formula for an egg-custard diet used in some Brazilian freshwater prawn hatcheries is given in Table 6.5.

As has been stated previously, prawn larvae do not actively capture their prey, and the ability of larvae to catch sufficient food relies on the frequency of encounter.

Table 6.5 Composition and nutritive value of egg-custard feeds for M. rosenbergii larvae used in Brazil. (Reproduced from Mallasen & Valenti 1998, copyright 1998 with permission of Blackwell Publishing.)

Ingredients

Wet weight %

Chicken egg

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