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Study on Histopathology and Infectious Microecology of Common Diseases in Cultured Half-smooth Tongue Sole (Cynoglossus Semilaevis Günther)

Author: ZhangZheng
Tutor: WangQingYin; WangYinGeng
School: Ocean University of China
Course: Marine biology
Keywords: Half-smooth tongue sole (Cynoglossus semilaevis Günther) Histopathology Infectious microecology Skin ulceration Ascites
CLC: S943
Type: PhD thesis
Year: 2012
Downloads: 262
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Half-smooth tongue sole (Cynoglossus semilaevis Günther) is one marine fishspecies native to northern China offshore areas. And also, it is another flatfish whichits farming forming industrial scale after Japanese flounder (Paralichthys olivaceus)and turbot (Scophthalmus maximus) in China. In this paper, epizootic investigationhas been performed and typical disease samples are selected for histopathology andinfectious microecology research in cultured half-smooth tongue sole by usingon-site investigations, paraffin section technique, microorganism cultivating,PCR-DGGE and PTS-454(high-through sequencing technique based on Roche454platform) methods respectively. The results of these studies will enrich the data offlatfish diseases research, and provide the fundamental works for constructinghalf-smooth tongue sole disease control and prevention techniques system. All theresults of this paper are as follows:1. The common diseases in cultured half-smooth tongue soleAll the diseased fishes for epizootic investigation in this paper are sampled infarms or derived from arrived samples for inspection from Shandong Peninsula, China.The results show that diseases occurred frequently and pose a threat to the sustainabledevelopment of half-smooth tongue sole farming industry. The investigation also findthat fin and tail rot, skin ulceration, subcutaneous abscess, ascites and enteritis werethe most common diseases in cultured half-smooth tongue sole in China. Thesediseases have conspicuous clinical epidemiologic characteristics and are easilyrecognizable in farming. There are no viral and parasitic disease fish in our collection samples.2. Histopathology of cultured half-smooth tongue sole typical diseasesAs the typical diseases, the fish associated with skin ulcer and ascites symptomare respectively chosen for histopathology analysis. The results reveal that mostorgans of skin ulcer fish exhibit varying organ lesion beside the ulceration on the body.The major organs pathological changes of diseased fish include muscle fiberspyknosis and focal ulceration, branchial lamella oedema and capillaries dilation withcongestion, red blood cells infiltration in the derma of the fin, the detachment of innernuclear layer and outer plexiform layer in the retina, tissues necrosis and ulcer in thehepatopancreas and kidney, dead red blood cells accumulation in the spleen, necrosisof myocardium and hemocyte and lymphocyte infiltration in the heart, detachment ofmucosal epithelium and lamina propria and focal epithelial tissues hyperplasia andulceration in gastrointestinal tract. The diseased fish associated with ascites also showdifferent pathological changes in most organs. Comparing to skin ulcer disease, thesefish organs lesions are relatively lesser degree. The major damage of organs indiseased fish with ascites symptom are: spot congestion in dermis, epithelium oedemaand cylindrical cell hyperplasia in branchial lamella, myocardium focal fracture,tissue focal necrosis in hepatopancreas, the fusion of glomerulu and renal interstitium,thrombosis and connective tissue hyperplasia of gallbladder wall, neural cellsvacuolar and granular degeneration existence in brain, lamina propria focal necrosis instomach and intestine. Surmising from the results, multiple organ tissues damage andmetabolic dysfunction or loss, this may be the ultimate cause of death in diseased fish.3. Microecology characteristics of cultured half-smooth tongue sole in outdoorpondThree healthy half-smooth tongue sole are randomly selected form the outdoorculture pond for correlation analysis of microflora in different fish organs, water, pondsediment and pellet feed using microorganism cultivating, PCR-DGGE and PTS-454(high-through sequencing technique based on Roche454platform) methods. The studies find that only vibrios can be isolated form fish intestine, water and pondsediment using traditional microorganism cultivating method. But the results ofbacteria isolation are not enough to support the correlativity analysis of microflora inthe samples. Using PCR-DGGE technique, the correlation of microbial communitiesin fish organs, water and pond sediment can be qualitatively analyzed. And microbialdiversity in these samples is also analyzed through the electrophoretic bandsrecovering and sequencing. But there are some deviations which can not be avoided inparallel experiment. According to the analysis of PTS-454results, we can confirm thatthe microbial community structure in half-smooth tongue sole different organs is verysimilar. It is also relevant to the microflora in pellet feed for feeding, while almostindependent from the microflora in water and pond sediment.4. Infectious microecology characteristics of diseased half-smooth tongue sole inindoor farming systemThe infectious characteristics of diseased half-smooth tongue sole respectivelyassociated with skin uler and ascites are also analyzed using the three aforementionedmethods. Three diseased fishes associated with skin ulceration symptom and onenormal fish in the same farming system as samples are derived from one indoor farm,and three diseased fishes associate with ascites and one normal fish in the samefarming system from another indoor farm. Bacteria can be isolated only from portionsof diseased fish focal ulceration and intestine. These becteria belong to Vibrios,Alteromonas, Pseudomonas, Shewanella, etc. It is still difficult to analyze thecorrelation of microbial community structure in the samples basing on these bacteriaisolation. However, the similarity between the microflora in different organs ofdiseased fish but different from normal fish organs are confirmed by PCR-DGGEmethod. The results also reveal the limited relationship of microflora betweenhalf-smooth tongue sole intenstine, water and pellet feed in indoor farming system.The water, pellet feed and four fishes are also studied the microbial communitystructure by PTS-454method. The results show that predominant strains in all fishorgans are similar and different from those in water and pellet feed. But the abundance of different predominant strains changes noticeably during the diseaseoccurrence. This means that the microecology niche of predominant strains reverseafter disease occurrence. Most of bacterial16S rRNA sequences obtaining byPTS-454can not find the similar data in NCBI GenBank.Summarizing these results, two suppositions are brought forward. First, in thecases of this paper, the predominant bacteria in all fish samples are almost the same.Obviously, there may be symbiotic microflora in cultured half-smooth tongue solebody. These bacteria are exclusivity and regardless of farming system, environmentand fish health changes. It can be colonization during the larval fish rearing stage.Second, in the indoor farming system, the microecology niche of these bacteriachanged in the fish body, which may be the direct cause of disease occurrence.

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CLC: > Agricultural Sciences > Aquaculture, fisheries > Fisheries Protection > A variety of fish diseases, predators,and its control
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