Simultaneous, 6-week feeding trials were conducted in which diets containing menhaden, corn, coconut and hydrogenated
menhaden oil at 7.0%, plus a diet containing 14%
menhaden oil, were fed to triplicate groups of juvenile red drum (Sciaenops ocellatus) at two different salinities (5 and 32%.).
Weight gain was significantly (p < 0.05) affected by diet and salinity. Fish fed the diet containing 14%
menhaden oil had the greatest
weight gain; whereas, fish fed the diet containing
coconut oil gained the least weight. Fish in brackish water had significantly greater
weight gain than fish in full-strength seawater over the 6-week period, although fish fed coconut and saturated
menhaden oil in brackish water had reduced survival. Dietary
lipid also significantly affected muscle and liver total
lipid, hepatosomatic index (HSI), and intraperitoneal fat (IPF) ratio, as fish fed the diets containing 14%
menhaden oil had higher values for all of these body condition indices.After the feeding trial, fish were subjected to a chronic cold tolerance assay. In the chronic trial, where temperature was gradually reduced over a 3-week period, fish fed the diets containing
menhaden oil had significantly lower median lethal temperatures (MLT) than those fish fed the diets containing coconut, corn and saturated menhaden
oils. No significant effects of cold exposure were observed on muscle and liver total
lipid. Cold exposure prompted a modification in lipid metabolism by lowering total
saturated fatty acids and raising (n - 3) highly
unsaturated fatty acids (HUFA) in the neutral
lipid of liver. Fish with the lowest MLT in the chronic assay exhibited signs of conserving (n - 3) HUFA and depleting (
n - 6) fatty acids [primarily 18:2 (n - 6)], resulting in higher (n - 3)/(n - 6) ratios in the polar
lipid of liver. These data suggest that the lower lethal temperature of juvenile red drum can be reduced through dietary manipulation involving the inclusion of high levels of dietary
lipid rich in (n - 3) HUFA.