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Tryptophan (TRP) is a precursor of serotonin (5-HT), which is known to affect food intake and aggression in vertebrates, including fishes. The effects of TRP-supplemented diets (0.25%, 0.5% and 1% of dry diet) on growth and cannibalism were evaluated in 38-day-old juvenile groupers (200-l tank, 750 fish per tank, 0.13 g in body weight and 2.16 cm in total length) over 10 days. HPLC analysis showed that TRP-supplemented diets were effective in increasing the levels of 5-HT in the brain of groupers. TRP supplementation resulted in slightly lower cannibalism than in controls. However, body weight and total length of TRP groups were significantly smaller than those of the control. The results indicated that cannibalism among juvenile groupers could be mitigated by the oral administration of TRP, in addition or in place of environmental factors, and the recommendation on supplementary TRP level to be used is 0.5% of dry diet. |
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