計畫目標：自1994年海鱺人工繁殖成功以後，由於具有快速成長的特性，因此海鱺可作為我國養殖產業今後在國內外市場與其他魚種(如鮭魚與鱈魚等)競爭的養殖魚種。海鱺在人工育苗階段經常發生大量死亡，經過一年試驗結果得知，除了卵圓鞭毛蟲外，細菌之分離株以弧菌、氣單胞菌及巴斯德菌為主。又由於箱網高密度的養殖，發生疾病頻度很高，經採樣檢驗結果發現寄生蟲主要為魚蝨與貝尼登吸蟲，而細菌則以以巴斯德菌和弧菌出現最為頻繁。本年度擬就所分離出之各種致病菌種，探討各種致病菌種對海鱺之致病屬性，觀察何種屬於急性發作，而何種屬於慢性發作；同時可了解何種菌為海鱺較主要的致病株，並進而探討該菌種之細胞外產物毒性，並進行細胞外產物初步分離純化，以了解有那些毒素會影響海鱺之存活。架構(重要工作項目)1.活化病原性菌株2.多種菌株交叉混合感染3.細菌酵素及溶血活性測定4.細胞外產物製備5.細胞外產物蛋白質及酵素活性測定6.細胞外產物毒性試驗7.細胞外產物之毒性因子分離試驗預期效益：由於目前有關本魚種細菌性疾病致病之基礎資料尚缺乏，因此有必要進行相關研究，作為日後疫苗開發及疾病防治之參考。 Project Object: Since the artificial propagation succeded in 1994, cobia with fast growing characteristic, has been recognized as a potential cultured species to compete with other marine fish such as salmon and cod in Taiwan and international markets. Outbreak of mass mortality frequently occurred in juvenile stage of cobia. The causative agents have been identified as species of Amyloodirium, Vibrio, Aeromonas and Pasteurella (Photobacterium damsela subsp. piscicida) after our investigation in the previous year. In cage culture with high density of cobia, the major species of parasites identified were sea lice and Benedenia sp. while major species of bacteria were Photobacterium and Vibrio. This year we intend to investigate the pathogenicity of the bacterial isolates and to identify the major virulent species for further studies on the toxicity of its extracellular products (ECP) in the fish. In addition, partial purified toxin(s) will be tested in the fish. Struction: 1. Activation of pathogenic bacterial strains. 2. Mixed infection with various strains. 3. Assays for bacterial enzyme and hemolytic activities. 4. Preparation of extracellular products (ECP). 5. Determination of ECP protein and enzyme activity. 6. Toxicity of ECP. 7. Purification of ECP toxic factor(s). Prospective: Owning to the lack of basic information concering bacterial diseases in the cobia, our present study is needed and will be useful for future development of vaccine and disease control.