小头鲔寄生鳍缨虫的分离及鉴定

海南陵水小型金枪鱼驯养基地在小头鲔(Euthynnus affinis)养殖过程中发现有寄生虫附着现象,文章对小头鲔寄生虫进行了分离、形态观察及18S、28S rRNA分子鉴定。结果显示,经18S rRNA分子鉴定,该寄生虫与Branchiomma sp.相似性为99.13%;而28S rRNA显示,该寄生虫与黑斑鳍缨虫B.nigromaculatum相似性为100%,与Branchiomma sp.(EF116223.1)相似性为99.12%。形态观察发现,该寄生虫虫体呈墨绿色、棕黄色或红棕色,具鳃冠,全长30~90 mm,寄生于小头鲔鳃弓后缘的体表及胸鳍中后部。该寄生虫由鳃冠、胸区和腹区组成,无钙质管,其消化道包括口、口腔、咽、肠、肛门等,与黑斑鳍缨虫存在少许生活习性和形态差别。因此,该寄生虫是否为鳍缨虫属(Branchiomma)、黑斑鳍缨虫(B.nigromaculatum),仍需进一步验证。该虫附着于小头鲔体表后,小头鲔摄食量明显下降,游泳速度加快,易受惊吓。采用甲醛浸泡具有良好的去除效果,去除后小头鲔成活率为75.9%。

Identification and isolation of parasite Branchiomma in ground-based culture of Euthynnus affinis

Parasites were observed during land-based farming of the small tuna(Euthynnus affinis)in Tropical Fisheries Research and Development Center,Sanya,Hainan.In this study,the parasite was isolated and morphologically observed,and 18S and 28S rRNA molecules were identified.The 18S rRNA showed 99.12%similarity to Branchiomma sp.(EF116223.1)and 28S rRNA showed 100%similarity to B.nigromaculatum.The parasite was found on the surface of the posterior margin of gill arch and middle and posterior part of pectoral fin of E.affinis.The body of the worm was dark green,brownish yellow or reddish brown,with a gill crown,and the total length was 30–90 mm.The parasite consisted of gill crown,chest and abdomen,but calcareous canal was not found.Its digestive tract included mouth,pharynx,intestine and anus.Therefore,the parasite might belong to Branchiomma and B.nigromaculatum,but further verification is needed.The infected fish reduced food intake significantly,accelerated the swimming speed,and were easily frightened.Formalin immersion had a good removal effect,and the survival rate of the fish after cure was 75.9%.