Studies on the mass mortality of the cultured grouper, Epinephelus septemfasciatus

양식(養殖) 능성어, Epinephelus septemfasciatus 대량(大量) 폐사(斃死)에 관(關)한 연구(硏究)

In the late summer of 1990 and 1991, mass mortality occured among cage-cultured grouper, Epinephelus septemfasciatus in south cost of Korea. The moribund fish didn't feed and became pale or dark chestnut colour and irregularly swimmed due to the loss of equilibrium, finally the diseased fish fell down side away on the bottom or the surface of cage showing the bent of body and died. The diseased fish showed the extensive hemorrahge in brain, the swelling of spleen and bile duct as the specific syptoms of internal organs. So the gill, skin and other organs of the diseased fish were examined for the presence of pathogenic parasites and bacteria. The parasitic Trichodina sp. were detected only from the gill lamella of the diseased fish, but these parasites seemed to be not a direct causative agents that induced the gross mortality of the cultured grouper. because these parasites were also observed in normal grouper, yellowtail, red seabream and rock bream co-cultured with the diseased grouper in same or near cages. In the viral examination, although isolation of the causative agent by the use of estabilshed cell Lines, RTG-2 and CHSE-214, was not succeed, the normal grouper inoculated intramuscularly with the filtered homogenate of the organs of the diseased fish showed the same external and internal signs with the naturally infected grouper. They died within a week. By using the naturally and the artificially infected fishes, electron microscopic observation revealed numerous hexagonal or polygonal particles in the cytoplasm of liver cells. Based on the these results, we suggest that the mass mortality of the cultured grouper would be occurred by the infection of a viral agent.

1. 자연감염(自然感染) 능성어는 외관적으로 먹이를 먹지 않고 분색이 옅은 밤색이나 짙은 밤색으로 변하며 몸이 휘어져 힘없이 가두리 바닥이나 수면에 누워서 폐사(斃死)하였는데, 해부(解剖)를 해보면 뇌출혈(腦出血)과 비장(脾臟) 및 담관(膽管)이 팽대(膨大)되어 있었다. 2. 자연감염어(自然感染魚) 아가미에서 Trichodina sp. 기생충(寄生蟲)이 다수 검출(檢出)되지만 대량(大量) 폐사(斃死)의 직접(直接) 원인생물(原因生物)은 아니며, 또한 병어(病魚)의 장기(臟器)에서 우점적(優占的)으로 분리(分離)되는 Vibrio속(屬) 세균(細菌)은 병원성(病原性)이 없는 해수상존(海水常存) Vibrio 균(菌)이었다. 3. RTG-2 및 CHSE-214 어류(魚類) 주화세포(株化細胞)에서 바이러스는 분리(分離)되지 않았지만, 병어(病魚)의 장기마쇄여과액(臟器磨碎濾過液)으로 인위감염(人爲感染)시켰을 때 자연감염어(自然感染魚)와 유사(類似)한 증상(症狀)을 나타내면서 폐사(斃死)하였다. 4. 자연감염어(自然感染魚) 및 인위감염어(人爲感染魚)의 간(肝) 세포질내(細胞質內) 공포부위(空胞部位)에 크기가 45-60nm 정도되며 육각형(六角形) 내지 다각형모양(多角形模樣)을 한 virion들이 무수히 존재하였다. 5. 따라서 1990년(年)과 1991년(年) 고수온기(高水溫期)에 우리나라 남해안(南海岸) 일원 해상가두리 양식장에서 사육중이던 능성어가 대량(大量) 폐사(斃死)한 것은 바이러스성(性) 질병(疾病)에 의한 것으로 생각된다.