Effect of dietary lipid levels on growth, feed utilization, body composition and serum metabolites of meagre (Argyrosomus regius) juveniles

The study investigates the effect of dietary lipids on growth of meagre (Argyrosomus regius) juveniles. Triplicate groups of fish (average weight ± SD, 229.7 ± 1.4 g) were fed for 110 days three isonitrogenous experimental diets (43% crude protein, dry matter) containing 13, 17, or 21% crude lipids. Body weight, total length and specific growth rate of fish fed the 17% lipid diet were significantly higher than that of fish fed the 13 and 21% lipid diets. Daily feed intake was not affected by the dietary lipid level, but there were significant differences in feed conversion ratio and protein efficiency ratio. There was no significant difference in condition factor, hepatosomatic or viscerosomatic indexes. Proximate analysis indicated that the lipid content of whole body and muscle was affected by the diets, whereas the other chemical components of whole body, muscle and liver were unaffected by the increase in dietary lipid content. Whole body and muscle of fish fed the 21% lipid diet showed significantly higher values of total lipids (whole body: 7.41 ± 0.45% and muscle: 0.64 ± 0.13%) than fish fed 17 and 13% lipid (whole body: 5.92  ± 0.12%, muscle: 0.37 ± 0.08% and whole body: 5.76 ± 0.23%, muscle: 0.31  ± 0.02%, respectively). Serum metabolites did not show significant differences among the three dietary lipid levels. Overall, the results indicated that the best growth performance was observed in fish fed the 17% lipid diet, whereas the increase of dietary lipid level from 17% to 21% had a negative effect on growth. In conclusion, meagre juveniles appear to have similar lipid requirements with other Mediterranean species and excess dietary lipid level should be avoided, since the increase from 17% to 21% resulted in higher fat accretion and impaired growth performance.