Estimation of dietary biotin requirement of Japanese seabass, Lateolabrax japonicus C.

A 9-week feeding experiment was conducted to determine the dietary biotin requirement of Japanese seabass, Lateolabrax japonicus C. Six isonitrogenous and isoenergetic purified diets (Diets 1-6) containing 0, 0.01, 0.049, 0.247, 1.238 and 6.222 mg biotin kg-1 diet were fed twice daily to triplicate groups (30 fish per group) of fish (initial average weight 2.26 +/- 0.03 g) in 18 fibreglass tanks (300 L) filled with 250 L of water in a flow-through system. Water flow rate through each tank was 2 L min-1. Water temperature ranged from 25.0 to 28.0 degrees C, salinity from 28.0 to 29.5 g L-1, pH from 8.0 to 8.1 and dissolved oxygen content was approximately 7 mg L-1 during the experiment. After the feeding experiment, fish fed Diet 1 developed severe biotin deficiency syndromes characterized by anorexia, poor growth, dark skin colour, atrophy and high mortality. Significant lower survival (73.3%) was observed in the treatment of deficient biotin. The final weight and weight gain of fish significantly increased with increasing dietary biotin up to 0.049 mg kg-1 diet (P < 0.05), and then slightly decreased. Both feed efficiency ratio and protein efficiency ratio showed a very similar change pattern to that of weight gain. Dietary treatments did not significantly affect carcass crude protein, crude lipid, moisture and ash content. However, liver biotin concentration (0-6.1 mu g g-1) significantly increased with the supplementation of dietary biotin (P < 0.05), and no tissue saturation was found within the supplementation scope of biotin. Broken-line regression analysis of weight gain showed that juvenile Japanese seabass require a minimum of 0.046 mg kg-1 biotin for maximal growth.