Effects of dietary lipid level on growth and lipid utilization by juvenile Atlantic halibut ( Hippoglossus hippoglossus, L.)

Abstract

A study was conducted to determine the efficiency of lipid utilization by juvenile Atlantic halibut ( Hippoglossus hippoglossus, L.). Triplicate groups of fish (average weight, 33.0 ± 0.3 g) were fed four isonitrogenous (56% crude protein, DM-basis) experimental diets containing 14, 18, 22 and 25% lipid for 13 weeks. The effects of dietary lipid levels on growth, feed utilization, body composition, nutrient and energy retention, tissue lipid accumulation and fatty acid composition were determined. Growth and feed conversion ratio were not affected by an increase in dietary lipid intake. Whole body lipid content increased from 24.9 ±0.8% to 31.6 ± 0.6%, reflecting the increase in dietary lipid level. Nitrogen and energy retention values did not show significant differences among treatments. Despite a large individual variability in liver lipid content, the liver of fish fed the 22% lipid diet showed significantly higher values (18.9 ± 3.7%) than fish fed 14 and 18% lipid (13.1 ± 1.3% and 12.9 ± 2.5%, respectively). Muscle lipid content was not significantly affected by an increase in dietary lipid content. The dietary fatty acid profile was reflected in both liver and muscle tissue. Higher eicosapentaenoic (EPA) and lower linoleic acid concentration in liver were observed with increasing fish oil levels. It appears that halibut juveniles can tolerate up to 25% dietary lipid; however, there are no beneficial effects in terms of growth and macronutrient retention beyond 14% dietary lipid level.