Studies on the Fatty Liver Diseases of Sciaenops ocellatus Caused by Different Ether Extract Levels in Diets

An experiment was conducted to study fatty liver disease caused by different ether extract levels in diets of juvenile Sciaenops ocellatus.Juvenile S.ocellatus(n=1,260;initial body weight approximately 2.73 g)were divided into nine treatment groups(triplicate groups per treatment)and fed in aquatic cases by a recirculated filtered rearing system;the temperature of the aquatic cases was maintained at 23.2±2.0°for 8 weeks.Nine kinds of diets containing different protein(38,42,46%)and ether extract levels(4,8,12%)were used.Results showed that the relative growth ratio and survival ratio of the fish fed on medium lipid diets(8%)or high ether extract diets(12%)were significantly lower than those of the fish fed on low ether extract diets(4%)(p<0.05).There was a positive correlation between the ether extract contents in hepatopancreas of fish and the ether extract contents of diets.At the end of the experimental period,the fish of the nine experimental groups suffered from different degrees of fatty liver disease and serious illness,and death occurred in a large number of fish fed on medium(8%)and high ether extract diets(12%)from the third test week;mortality was highest in the fifth test week.The ill S.ocellatus showed symptoms of loss of appetite,lack of movement,black skin,and weight loss and eventually died.The main pathological change in ill fish was fatty liver disease.Their hepatopancreas were swollen and pale,accompanied by fatty degeneration,fatty necrosis of hepatocytes,and atrophy of the pancreas.Ultrastructural changes showed the presence of many lipid droplets and granules in the mitochondria,endoplasmic reticulum,and cell plasm of hepatocytes.Study results indicated that all the nine kinds of diets with different lipid or protein levels could cause nutritional fatty liver disease in juvenile S.ocellatus.The pathological severity and serious level of fatty liver disease in the tested fish positively correlated with the contents of the ether extract,but not with those of protein,in test diets.The increase in the level of ether extract in test diets was responsible for the direct cause of illness or death in juvenile S.ocellatus.