Requirements for enriched Artemia by freshwater prawn larvae

In contrast to penaeid shrimp, the (n-3) HUFA requirements of M. rosenbergii were not expected to be very critical, because they spend most of their life in fresh water. Roustaian et al. (1999) concluded that the larvae of M. rosenbergii have sufficient capability to convert dietary linoleic acid (18:2 n-6) and linolenic acid (18:3 n-3) to arachidonic acid (20:4 n-6) and EPA to meet larval demand for HUFA, although there was no assimilation and consequent tissue storage of DHA. As a result it was claimed that non-enriched Artemia can fulfil the nutritional requirements, providing a greenwater system is used. These assumptions, however, were in some way contradicted by studies at the Artemia Reference Center of Ghent University, where M. rosenbergii larvae were reared on Artemia alone in a clearwater circulating system. Devresse et al. (1990) demonstrated that pronounced improvements in growth, survival, metamorphosis synchrony and stress resistance were obtained whenArtemia enriched with n-3 HUFA emulsions were administered (Fig. 6.6). Also, the levels of these essential fatty acids (EFA) in the larval tissues increased as a function ofthe dietary regime, as was demonstrated by Roustaian et al. (1999). This n-3 HUFA requirement was further confirmed by Romdhane et al. (1995), who documented a minimum requirement of 35 mg/g n-3 HUFA in the freshwater prawn larvae diet. More recently, Rani et al. (2006) fed Artemia nauplii enriched with cod liver oil and/or Lactobacillus to prawn larvae. The first PL appeared 7 to 8 days earlier and 95% ofthe PL 11 to 12 days earlier in the emulsion-enriched groups than in the control or probiotic-only groups. Survival was highest in the group fed Artemia enriched with both the probiotic bacteria and codliveroil. However, deCaluwe etal. (1995) demonstrated that these EFA effects in larval prawn are also a function of the broodstock diet. Larvae obtained from M. rosenbergii females fed a HUFA-fortified diet performed equally well on non-enriched as on enriched brine shrimp.

Feeding vitamin C-enriched Artemia did not result in an enhanced freshwater prawn hatchery output (Merchie et al. 1995b). However, a significantly positive effect was again demonstrated on the physiological condition of the PL, as measured by a salinity stress test. A noticeable drop in the vitamin C level of PL, compared to larvae, indicated a specific need for ascorbic acid during metamorphosis, a stressful period. It therefore is likely that under suboptimal rearing conditions (stress situations), high vitamin C supplementation will enhance production characteristics. In this respect, Cavalli et al. (2000); Fig. 6.7) developed a standardised technique based on ammonia toxicity for the evaluation of the postlarval quality of hatchery-produced M. rosenbergii, which proved far more sensitive than the more common salinity stress test. Using this criterion, these authors were able to clearly demonstrate that, from larval stage III onwards, larval quality was superior in the prawn culture tanks receiving HUFA/vitamin C-enriched Artemia compared to the cultures fed non-enriched brine shrimp.

In view ofthe research findings reviewed above, it is suggested that commercial freshwater prawn hatcheries would benefit from the use of enriched Artemia throughout the culture period, unless other HUFA- and vitamin-rich supplemental feeds are administered from stage V onwards.

Recent live feed applications for freshwater prawn larval rearing include uploading Artemia with probiotic bacteria and hormones. Keysami et al. (2007) fed prawn larvae

Metamorphosis (days)

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