Study on the Winter Mass Mortality of red sea bream, Pagrus major in South sea area

Ocean Research Division, National Fisheries Research and Development Institute, 408-1 shirang Gijang,Busan 619-705, KoreaPathological symptoms and hematological parameters of red sea bream, Pagrus majorand water temper-ature in the culture ground was investigated to clarlify the cause of winter moratility. Dead fish showedgreen liver and accumulation of ascites in the cavity. A few Bivagina taiwere also found on the gill buteither bacteria or virus were not.When hematological parameters from fish taken before/after the winter mortality were compared, bloodglucose, serum AST and ALT, and total cholesterol, trigyceride and total protein were significantlydecreased in the fish after the winter mortality. These results may explain that the nutritional level of fishwas decreased because fish could not fed during winter season. According to the CORI monitoring system operating by KODC, NFRDI a long term water temperaturefrom Dec. 25, 2005 to Feb. 24, 2006 (60 days) were exposed the low water temperature environments to thered sea bream. First of all, mass mortality began at Sarayngdo where low temperature below 8℃continued for 42 days.The winter mortality did not occured in the depths of 9 m to 19.2 m where difference of water temperaturein the surface and bottom was only within 0.1℃. But in the depth of 7.5 m to 11 m winter mortality occuredwhere water temperature in the surface and bottom showed much variation ranged from 0.2 ℃to 1.4℃.From these results, great difference of water temperature in the surface and bottom of the culturing areamight results in winter mortality of red sea bream.Key words: Mass Mortality, Winter season, Red sea bream, South sea area