Correlation Between Bacteria Associated With Customary Feed And Diseases Occurrence Of Cultured Turbot Scophthalmus Maximus

Turbot, scophthalmus maximus(L.) was introduced from the U.K. to China in 1992. Since then, turbot had been extensively cultured because of its special biological characteristics and becoming an important industry rapidly along the coast of north China. The cultured area of turbot had arrived at more than 500×104 m2 and production attained nearly to 5×104 tons from the 700 cultured farms by the year of 2005, which had realized RMB 7 billion totally. Even though, with the rapid development of turbot aquaculture, as a result of over large density, resulting in massive reproduction of pathogenic bacteria, in that many of diseases occurred frequently, causing massive mortalities and economic losses. The problem to the diseases had limited the healthy, stable and rapid development of turbot aquaculture.In order to find out the real origin of pathogenic bacteria which caused the disease of cultured turbot, during 2005 to 2007, many of cultured systems of turbot in Shandong province were investigated, including well water, rearing pond water, feed and sicken turbot from these cultured farms which suffered from pathogenic bacterial invasion. Among the investigation of many cultured farms of turbot, the investigation showed that the feed associated with bacteria account for about over 90% of all feed of these investigated farms, especially these feed raw fish, the amount of bacteria comes to excessively 106. In the process of investigation in May 2006, An outbreak of ascites syndromes disease of the cultured turbot occurred in an indoor farm in Yantai. Through investigating bacteria for well water,rearing pond water and feed raw fish derived from the whole cultured system by the means of morphological features, found that the bacterium RF-1 associated with raw fish had the highest similarity to the bacterium FS-1 from the sicken turbot, Artificial challenge test demonstrated that the bacterium RF-1 and the bacterium FS-1 had the same infection symptoms for the healthy turbot .The further research, such as the traditionally physiological and biochemical test, API-ID32E test and 16SrRNA sequence analysis had also carried out. Concluded that the bacterium RF-1 and the bacterium FS-1 were V.alginolyticus. which indicated that the bacterium RF-1 was the real origin of the causative pathogen of disease ascites syndromes.The cultured turbot of the three farms, Laizhou, Penglai and Weihai suffered from severe white feces disease. After surveying, found that the three cultured farms utilized the same feed pellet. Using the above research methods, the results showed that the three kinds of pellets had the same bacterium KL-1 to the bacterium BB-1 from the sicken turbot. Artificial challenge test proved that the two strains had same infection symptoms to the healthy turbot, By the mean of the above identification methods, the two strains were Pseudoalteromonas sp. Drug sensitivity test for the four strains had been carried out, the results indicated that the strain FS-1 from the raw fish had identical sensitivity for antibiotics to the strain FR-1, the strain BB-1 to the strain KL-1. From the bacteriological analysis, quantitatively the pellet was better to raw fish.The animal diets also had been investigated on the basis of the above work. Although the relationship between the bacteria associated with the animal diets, including rotifer and Artemia sp, and the diseases of cultured turbot was not ascertained, the amount of bacteria is numerous, particularly the rotifer ,which comes to 1010CFU/g. In the course of investigation for bacteria of the whole cultured system in one Weihai cultured farm, found that 90% of the bacteria associated with the frozen Artemia was vibrio.sp. The further studies on pathogenicity of these bacteria isolated from the Artemia was not carried on, but it could be said that these dominant bacteria is related to the diseases of infant turbot. In addition, another seed breeding farm of barfin flounder verasper moseri suffered from ascites syndromes disease, the results of investigation for the entire system displayed that the disease was caused by three dominant strains A,B and C, isolated from the sicken infant barfin flounder, which was respectively similar to another three strains LH-1,LH-2 and LH-3 from the rotifer.So we can infer that the strains LH-1,LH-2 and LH-3 may be the real origin of the strains A,B and C. We strongly advised that the healthy and aseptic culture of animal diets be strengthened, which is much significant to the healthy aquaculture of young turbot.In May 2006, a kind of unusual disease occurred in a seed breeding farm of Senegalese sole Solea senegalensis in Laizhou, the symptoms displayed that the seedlings of Senegalese sole had become dark completely and been death suddenly in short time, the mortality rate was nearly 100%. As far as this phenomenon is concerned, the bacterial investigation of the whole breeding system had been carried out. The results indicated that the strain SN-1 isolated from the sicken Senegalese sole had the highest similarity to the strain M-1 from the microecological agents(MIC). The two strains were identified as Vibrios through culturing of bacteria in TCBS medium.The sensitivity of bacteria for antibiotics also had carried out ,the results demonstated that the two strains SN-1 and M-1 had srongly resistance to the antibiotics, so it may be a kind of engineering bacterium.In this paper, we discussed the correlation between bacteria associated with the customary feed and diseases of cultured turbot, in order to provide theoretical foundation and reference of treatment and prevention of diseases for healthy aquaculture of turbot.