| Myxozoa is a kind of metazoan with small morphology and highly degraded structure and organization,belonging to the Phylum Cnidaria.The host is mainly freshwater and marine fish.A small number of fish diseases caused by myxozoans often cause a large number of deaths in farmed fish and bring huge losses to the aquaculture industry.In this study,during the investigation of parasitic myxospores in fish in Jiangsu Province,several Myxobolus spp.found from different tissues and organs of silver carp of Taihu Lake,and several actinospore species from gibel carp pound were description and identification by morphology,histopathology and molecular methods.Moreover,the Percoll density gradient centrifugation method was used to isolate and purify Myxobolus honghuensis from diseased fish.and the survival rate of M.honghuensis was identied by Green nucleic acid stain to choose effective drugs.(1)During April 2018 to July 2019,ten actinospore types were found in the oligochaete Branchiura sowerbyi Beddard.Based on morphological characteristics,they were identified belong to six collection groups,including one Raabeia-type,two Aurantiactinomyxon-types,two Neoactinomyxum-types,two Triactinomyxon-types,two Echinactinomyxon-types and one Hungactinomyxon-type.The present study describes six of them,Triactinomyxon type HZ,Triactinomyxon type DF,Echinactinomyxon type LY1,Echinactinomyxon type LY2,Neoactinomyxum type LY1 and Hungactinomyxon type DF.Blastn search indicated the SSU rDNA gene sequences that Triactinomyxon type HZ and Triactinomyxon type DF have the highest homology similarity with Triactinomyxon type CZ,93.39%and 94.48%;Echinactinomyxon type LY1 and Myxobolus lentisuturalis have the highest similarity(96.88%,AY119688);Echinactinomyxon type LY2 has the highest similarity with Hungactinomyxon type 1(97.86%,AY779062);Neoactinomyxum type LY has the highest similarity with Thelohanellus sp.(92.48%.MK412938);Hungactinomyxon type DF has the highest similarity with Hungactinomyxon(99.41%-99.64%).Phylogenetic analyses showed that Triactinomyxon type HZ and Triactinomyxon type DF were clustered on the Chloromyxidae subclade;Echinactinomyxon type LY1 and Echinactinomyxon type LY2 were clustered in the Myxobolus clade;the Neoactinomyxum type LY1 was clustered in the Thelohanellus clade.(2)Drug screening results found that drugs such as Eucalyptus oil,artemisinin,and trichlorfon have no effect on the survival rate of the Myxobolus honghuensis at concentrations of 0～512 μg/mL.At a concentration of 512 μg/mL in the high-concentration group of chlorpheniramine hydrochloride,it had a certain killing effect on the Myxobolus honghuensis.The concentration of Oregano oil increased from 0-1 μL/mL,and the spore killing effect gradually increased.Further analysis of the effective components in tallow found that as the concentrations of Carvacrol and Thymol,the concentration of carvacrol was 0.5 μL/mL,the spore survival rate was only 2.76%,and the concentration of thymol was 512 μg/mL,the spore survival rate was 19.18%.Carvacrol to cells’ LD50 was 118μL/mL(24h)and 0.086 μL/mL(48h);Acute toxicity experiment of Carvacrol to allogynogenetic crucian carp,the LD50 was 1148.32 mg/kg.(3)In the investigation of the parasitic myxozoans of silver carp in Taihu Lake,three Myxobolus spp.were found.Among them,two kinds of Myxobolus spp.infected kidney of silver carp were identified as Myxobolus lieni(Nie et Li,1973)and Myxobolus varius(Achmerov,1960)by morphological characteristics,host,and infection site;M.lieni infects the intraepithelium of renal tubular.M varius is distributed in the renal interstitium and is surrounded by a large amount of hemosiderin.A Myxobolus sp.Infected the pharynx of silver carp.The molecular sequence in NCBI by Blastn alignment found that there were no species with the same sequence of the three Myxobolus spp.;phylogenetic analysis showed that the three Myxobolus spp.were clustered in one branch,forming a separate clade in the cyprinid-infecting myxozoans. |
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