The effect of dietary taurine and its potential biosynthesis on juvenile grey mullet (Mugil cephalus) performance

The grey mullet is a catadromous species that spawns in the taurine-rich seawater environment, followed by the young fish generally migrating to less saline, low taurine waters during the larva-juvenile transition. Consequently, this study aimed to (1) determines whether there is a dietary taurine requirement in juvenile grey mullet for enhanced growth and (2) the potential for taurine biosynthesis. The experimental system consisted of sixteen 400-l V-tanks, where filtered, UV-treated ambient seawater (40 ‰) entered the bottom of the tanks at a rate of 7 tank exchanges/day. This allowed the testing of four 1 mm pelleted diets (0, 0.5, 1.0, and 2.0% taurine DW diet) in replicates of 4 tanks/treatment for 58 days. Grey mullet juveniles demonstrated (P<0.05) a specific requirement for a 0.5% taurine DW diet for improved growth. Fish fed the taurine diets displayed populations with a markedly (P < 0.05) higher average number of surviving fish (23.4±1.1) of moderately sized (10- 20 g) cohorts than smaller (< 10 g) individuals (12.5±1.1). In contrast, the fish fed the taurine control (0% taurine) exhibited similar average numbers of small and moderate sized fish (18.0±3.6-20.0±4.1). Dietary taurine accumulated highly (P<0.05) in the muscles in a dose dependent manner but less so (P<0.05) in eyes, and liver. The gene expression of liver cysteine sulfinic acid decarboxylase (CSD) exhibited an upregulation (P<0.05) with taurine diets from 0 to 1% but was down regulated (P<0.05) in fish fed the 2% taurine DW diet.