The Green Liver Syndrome Is Caused by Taurine Deficiency in Yellowtail, Seriola quinqueradiata Fed Diets without Fishmeal

Abstract

The causes of both green liver syndrome and inferior growth performance of yellowtail fed diets without fishmeal (FM) were evaluated in relation to dietary taurine concentration and activity of the hepatic taurine biosynthesizing enzymes. Juvenile yellowtail were fed for 41 weeks on non-FM diets based on 58% soybean protein, supplemented with graded levels of taurine. A reference diet based on 53% FM was also tested. Fish fed non-FM diet without taurine supplementation resulted in inferior growth performance, low feed conversion, higher mortality and anemia, and also greater incidence of green liver. The liver of this had significantly the lowest level of taurine and the highest concentrations of bile pigments among the dietary groups (P<0.05) . However, taurine supplementation to non-FM diets dramatically improved the situation. Furthermore, the hepatic taurine biosynthesizing enzyme activities in all the dietary groups were quite low irrespective of the dietary treatments and hepatic taurine concentrations. These observations indicate the necessity to supplement taurine to non-FM diets, since yellowtail cannot synthesize taurine sufficiently. The appearance of green liver in fish fed non-FM diets is possibly due to impaired excretion of bile pigments from liver into bile, and hemolytic biliverdin overproduction linked to dietary taurine deficiency.