Identification And Aethionlogical Of Pathogentic Bactetia Of Cultured Turbot (Scophthalmus Maximus)

Scophthalmus maximus is one of the most important commercial species in Europe which came of England and it was introduced into China in 1992.It has lots of strong suits,for example: it is seasoned with low temperature,it grows fast,it's flesh is very delicious and so on and it has came to be one of eximious aquiculture in Europe.After achieving technological breakthrough on the fry domestication,broodstock rearing ,artificial seed and compound feeds ,the fish was extensively cultured along the coast in north China and it became the fourth aquiculture tidal wave. It has brought tremendous economical and societal benefits.Whenas on account of the hugh stocking density, misgovernment , diseases especially bacteroidal diseases occurred continually and have caused high-level mortalities and loss.It has astricted the aquiculture of Scophthalmus maximus.A dominant strain of bacterium causing red body of turbot was isolated from the diseased turbot and designated as H1.In artificial infection test ,all fish of the experimental group died in 15 days after intramuscularly injected with high bacterial suspention(1.41×109CFU/mL), and the low bacterial suspention(1.41×CFU103/mL)did not cause any death, while the control group showed no signs all through the experimentation. The LD50 was calculated as 2.82×105CFU/mL.The moribund experimental fish had similar gross signs to the natural infected fish. The bacterium re- isolated from the challenged fish also had the same characteristics as H1, which proved that the isolated H1 was the pathogenic bacterium that triggered this red body disease. Different methods were used to identify the pathogenic bacterium. The bacterium is negative, rod in shape, peritrichous flagella under electronic microscope. Traditional biochemical identification revealed that H1 exhibited relatedness to Edwardsiella tarda, while the identification result by ID32E system indicated that H1 was E. tarda with 99.9% reliability . It's 16S ribosomal RNA gene sequences were analyzed , and it is shown from the anlysis results that this bacterium strain has a close phylogenetic relation (99%)to E.tarda. In summary, the pathogenic bacterium was identified as E. tarda. The 16S-23S rDNA IGS was amplified with the universal primers,and the PCR primers for the 16S-23S rDNA IGS was designed witch was specific to E. tarda.It revealed positive amplification to E. tarda ,whereas other bacterial species were negative,with the dedication limit of 7.2×103CFU/mL.In an investigation,we found another Edwardsiella tarda which caused Turbot to death.The symptoms were eye tumefaction, inflammation, ascites and the presence of a purulent fluid which were the main macroscopic lesions observed. A gram-negative, rod-shaped bacterium was isolated from the infected fish, and was proved to be virulent to turbot.Based on the biochemical characteristics tests and 16S rDNA sequencing , the bacterial pathogen was identified as E. tarda. It's LD50 was calculated as 1.35×105CFU/ml.Exophthalmia disease is one of diseases which often occurred in reared turbot on coastal regions of north China, it pronounced unilateral or bilateral exophthalmia and haemorrhage hyperaemia on the mouth. The further aetiology analysis indicates that this disease was caused by bacteria. One bacterial strain was isolated from the diseased turbot .Based on the results of searching NCBI database and 16s rDNA Cluster Analysis, this strain was classified as Enterococcus casseliflavus. Micrograph of histopathology revealed eyeball necrocytosis, retina and choroids tissues putrescence and periorbital oedema.Five strains were isolated from Scophthalmus maximus whose thorn was floccosoids . The organization around the bristles was first infected, and then the floccosoids taked form , some floccosoids connected into a slice .After days inner illness spreaded comparatively quickly , the death rate reached 100%. In the artificial pre-infection test, only B1(Bacillus subtilis) and B3 Rhodococcus erythropolis could cuased the fish to derth, others (B2/4: Psychrobacter nivimaris;B5: Pseudoalteromonas elyakovii) couldn't beget any symptoms.So Bacillus subtilis and Rhodococcus erythropolis were considered the pathogeny of the disease.