| Allogynogenetic crucian carp (Carassius auratus gibelio) is the descendant ofsilver Prussian carp () and Xingguo red common carp (). The area of Yangzhou,Jiangsu province is the main producing area of Allogynogenetic crucian carp whereprovide a good deal of fry for the breeding area of Allogynogenetic crucian carp. Thebreeding season of Allogynogenetic crucian carp is from late April to middle May.Inthe early June of recent years, a species of myxosporean what caused cystsonsurface of fry of Allogynogenetic crucian carp is found. This disease leads thehosts’body deformity, slim down, swimming hard and even mass mortality. Th-ecumulative mortality rate is about10%to60%. Mass mortality and selling difficult ofthe disease fish brings the huge economic losses to the fry breeding farmers.Therefore, in order to provide the foundation of study of this myxosporean andcontrol the disease, it is necessary to have a study of the pathogenandhistopathology changes in different period.In this paper, myxosporean is used as sample which caused this disease to findthe minimum effect and most precise measure condition to the spore of myxosporean.Normal saline is used making fresh spores’ smear to measure the myxosporean’sshape, and measurement result is used as comparison group. Measurement result ofspores’ length, width, thickness and polar capsules’ length and width from freshspores’ smear made by distilled water and24hours fixation in neutral formalin,70%ethyl alcohol,95%ethyl alcohol, Bouin’s solution,2.5%glutaraldehyde, A.F.Fsolution and G.A.F solution is analysised by statistical methods. The result shows thatdistilled water will make spores slight expansion, although which have less effect tothe morphology of myxosporean. All fixatives have more or less effect to themorphology of myxosporean. Neutral formalin, ethyl alcohol, Bouin’s solution,2.5%glutaraldehyde caused shrinkage of spores. Among these fixatives,95%ethyl alcohol lead the spore shrink most heavily,70%ethyl alcohol and Bouin’s solution causedless shrinkage than95%ethyl alcohol but more shrinkage than other fixatives.2.5%glutaraldehyde is the best fixative because it has the least effection to the morphologyof myxosporean. Meanwhile, neutral formaldehyde can be used instead of2.5%glutaraldehyde.With the identification method confirmed above. Thelohanellus wuhanensis Xiaoet Chen,1993infecting skin and fin of fry of Allogynogenetic Crucian Carp(Carassius auratus gibelio) was isolated. To augment the original description, T.wuhanensis is redescribed here by morphological and molecular biological datas.Mature spores of T. wuhanensis are melon seed,21.92-26.93(24.55±0.95) μm longand11.43-15.48(13.72±0.98) μm wide in frontal view and thick spindle shape,10.83-14.14-(11.80±0.45) μm thick in lateral view. Polar capsules are approximatelyspherical,9.64-12.79(11.54±0.68) μm long and8.14-10.28(9.12±0.45) μm wide,containing polar filaments coil7-10turns. Some new characteristics of T. wuhanensisare found. Mucous envelopes only surround posterior part of spores. Vertical distancefrom front end of spores to mucous envelope is5.03-16.69(10.37±2.36).“V”-shapededges marking on the spores’ shells. Spores have asymmetric front ends, one of whichshell has a protuberance on the the front end. Sutural ridges are straight. Total lengthof polar filaments are measured. Phylogenetic analysis indicates that Thelohanellusand Myxobolus have a very close genetic relationship. It is reasonable that bothThelohanellus and Myxobolus belong to the family Myxobolidae.The early stage of this disease is from late May to mid-June. At this time, verysmall cysts only cause the skin slightly elevated. Subsequently, cysts increases, andthe surface of cyst distribute bits of black spots. Oval cyst is located in the looseconnective tissue of dermal layer of skin. Loose connective tissue surrounding cysts ishyperplastic, where can be seen hyperplastic melanocytes and hyperplastic capillaries.Cyst membrane is made up by connective tissue. Early sporonts are mostly locatednear the cyst membrane. With the development, sporonts will enter into the cyst. Thesporonts in the internal of cyst will develop to mature spores earlier than the sporontsnear the cyst membrane. Mature spores are developed by disporous sporonts ortetrasporonts. The hardest period of this disease is during late mid-July to mid-August.At this time, cysts are full of spores. There are large and dense black spots on thecysts’ surface. The diameter of the largest cyst is more than1.7mm and the number ofthe cysts in one fish is up to30. Beside skin and fins, the cysts and spores are not found in other organs. Large cysts cause the scales bent. Some cysts will be deformedby scales’ extrusion. Sometimes two cysts close to each other and fuse together.Melanocytes are more than the early stage. Kind of unknown objects are located atnearby of some cysts. There are a large number of mature spores in the cysts. At thesame time, sporonts still exist near the membrane. After mid-August, the disease isbeginning to recovery. Meanwhile, cysts are beginning to shrink and disappear. At thistime, the color of the cyst surface is blacker because of the added melanocytes. Thereare only mature spores in the cysts. With recovering, the cyst membrane which iscomposed by connective tissue is replaced by epithelial cells. Then, gaps appear onthe membrane and spores will outflow from the gaps. After the disappearance ofspores, cysts will still exist for some time. When cysts disappear, the hyperplasticconnective tissue, melanocytes, and the unknown objects still exist, and free sporescan be seen in the connective tissue. The cysts disappear after mid-September,however the nidus marks are still visible. |
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