Craig, S.R., Washburn, B., Gatlin, D.M.
Abstract:
Previous experiments with juvenile red drum, Sciaenops ocellatus, have indicated that this species performs well when fed diets containing high levels of lipid. However, they are prone to store excess energy in the liver and peritoneal cavity, which has raised concerns as to whether this storage in the liver can lead to metabolic disorders in terms of impaired liver function.
An 8-week feeding tria1 was conducted to evaluate the effects of different dietary lipid levels on weight gain, feed efficiency, biological indices and liver composition of juvenile red drum. Diets were formulated to contain 40% crude protein from solvent-extracted menhaden fish meal and 0, 7, 14 or 21% lipid from menhaden fish oil. Available energy levels of the diets increased with lipid supplementation and ranged from 3.13 to 4.11 kcal/g diet. A mixture of n-3 highly unsaturated fatty acids was added to the basal diet to satisfy the essential fatty acid requirement of red drum. These diets were fed to groups of 25 juvenile red drum initially averaging 7.3 +/- 0.18 g/fish in a recirculating culture system composed of 110-1 glass aquaria. At the end of the feeding trial, weight gain and feed efficiency were calculated and 16 fish from each treatment were utilized to measure hepatosomatic index (HSI) and intraperitoneal fat (IPF) ratio values. Additionally, livers were rapidly removed and divided into subsamples for the determination of malondialdehyde (MDA) formation.
Weight gain and feed efficiency were significantly (P </= 0.05) affected by dietary lipid level, with values ranging from 312% of initial weight and 0.45, respectively, for fish fed the basal diet to 442% of initial weight and 0.55, respectively, for fish fed the diet containing 7% total lipid. The HSI and IPF ratio values also were significantly affected by lipid level with the lower values found in fish fed the basal diet and highest values observed in fish fed the diet containing 21% total lipid. Total lipid in diet also significantly affected MDA formation in the liver, indicating that as dietary lipid level increased there was a concomitant increase in lipid oxidation products in the liver. From these data, red drum appear to perform best in terms of weight gain, feed efficiency, fat deposition and liver composition when fed diets with total lipid levels ranging from 7 to 14% of dry diet, although no overt detrimental effects were observed in fish fed diets containing as much as 21% lipid. Liver function enzyme assays are currently being performed to determine the potential metabolic effects of dietary lipids in red drum.
(Department of Wildlife and Fisheries Sciences, Texas A&M University System, College Station, Texas 77843-2258, USA)
***************