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 °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 μg 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.