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Striped trumpeter have a complex and extended larval phase and are difficult to culture. Two experiments were conducted in replicated, 300-l hemispherical tanks to determine if larval survival, growth, bacterial or fatty acid profile were improved by feeding non-enriched rotifers or rotifers enriched with algae or commercially available products, as well as the effect of an antibiotic, oxytetracycline (OTC). Larvae were stocked at 25 l− 1 and 15 l− 1 and reared until Day 16 and Day 19 in Experiments 1 and 2, respectively. In Experiment 1, the feeding treatments were non-enriched rotifers, or rotifers enriched on algae, DHA Selco (a fish oil based emulsion) or RotiMac (dried Schizochytrium). There were no significant differences in mean survival (± SD) across treatments, which were generally low at 14.6 ± 5.2%. Larvae reared on rotifers fed DHA Selco and RotiMac, had significantly higher proportions of incorporated DHA but no significant increase in growth. In Experiment 2, larvae were fed rotifers enriched on DHA Selco or AlgaMac 2000 and reared with or without the daily addition of 25 mg l− 1 OTC. At Day 19, there was significantly higher survival for larvae reared on AlgaMac 2000 and OTC, (37.4 ± 5.6%), than DHA Selco and OTC, (16.0 ± 7.4%), AlgaMac 2000 without OTC (7.0 ± 8.0) and DHA Selco without OTC (3.3 ± 1.2). Larvae reared with OTC were larger (279 ± 58 μg and 7.4 ± 0.2 mm) than without OTC (177 ± 40 μg and 6.3 ± 0.2 mm). The addition of antibiotics did not significantly influence fatty acid profiles of larvae. There were no significant differences in the percentage of DHA, 27.6 ± 2.8%, EPA 4.6 ± 1.0% or ARA 4.9 ± 0.4%. Larvae reared with OTC had significantly less ‘grey gut’ (a measure of intestinal dysfunction). The results indicated that bacterial infection was a major source of mortality in striped trumpeter larvae and compromised larval growth. Assessment of the bacterial flora indicated that antibiotic use reduced the bacterial load, but did not eliminate potential pathogens. Our study suggests that microbial control has a greater influence than lipid nutrition on the survival and growth of larvae during the rotifer feeding stage. |
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