洄游型、淡水型和陆封型刀鲚的寄生蠕虫群落结构

由于对淡水环境的适应和江湖阻隔,部分洄游型刀鲚(Coilia nasus)分化成淡水型和陆封型,为寻找区分洄游型、淡水型和陆封型这3种生态型刀鲚的寄生虫标志,并分析其寄生蠕虫群落结构特征,本文调查了3种生态型刀鲚鳃部、胃、肠和幽门盲囊中寄生蠕虫的种类和感染情况。共发现10种寄生虫,包括鳃上3种单殖吸虫:林氏异钩铗虫(Heteromazocraes lingmueni)、细长嗜鳀虫(Helciferus tenuis)和长江中华钩铗虫(Sinomazocraes changjiangensis);胃部1种复殖吸虫:鲚套茎吸虫(Elytrophallus coiliae);肠道3种线虫:简单异尖线虫(Anisakis simplex)、对盲囊线虫(Contracaecum sp.)和胃瘤线虫(Eustrongylides sp.),以及肠和幽门盲囊的3种棘头虫:陈氏刺棘虫(Acanthosentis cheni)、鲇异吻钩棘头虫(Arhythmacanthus parasiluri)、长江傲刺棘头虫(Brentisentis yangtzensis)。林氏异钩铗虫和陈氏刺棘虫在3种生态型的刀鲚中都有较高的感染率和平均丰度;海水性寄生虫细长嗜鳀虫、鲚套茎吸虫和对盲囊线虫只感染洄游型刀鲚,可作为区分洄游型刀鲚的寄生虫标志;淡水性寄生虫长江中华钩铗虫、鲇异吻钩棘头虫和长江傲刺棘头虫只在淡水型刀鲚中发现,可作为淡水型刀鲚的寄生虫标志。洄游型刀鲚的物种丰富度和Brillouin多样性最高,分别在1.25和0.19以上,淡水型刀鲚的较低,分别为0.79~1.12和0.10~0.12,陆封型刀鲚的最低,分别在0.66和0.02以下,这主要是由于淡水型和陆封型刀鲚中海水性寄生虫大部分丢失,以及淡水性寄生虫感染率和平均丰度都较低造成的。盐度降低和中间宿主缺乏是导致淡水型和陆封型刀鲚中海水性寄生虫丢失的主要原因;而淡水性寄生虫较低的感染水平可能是由于其对新宿主的适应时间较短;地理隔离可能是陆封型刀鲚中寄生虫群落多样性最低的另一重要原因。

Helminth Communities in Coilia nasus from Anadromous, Freshwater and Landlocked Stocks

Three ecotypes of Coilia nasus were identified: the anadromous stock migrated between the Yangtze River and sea, the freshwater stock resided in the Yangtze River and its adjoining lakes, and the landlocked stock in lakes isolated to the Yangtze River. In order to find parasite indicator to separate the three stocks of C. nasus, species composition and diversity of helminth communities were investigated. A total of 10 species of helminths were found in 407 C. nasus from the 9 sampling localities: 3 of monogeneans, Heteromazocraes lingmueni, Helciferus tenuis and Sinomazocraes changjiangensis in the gills; 1 of digenean Elytrophallus coiliae in the stomach; 3 of nematodes, Anisakis simplex, Contracaecum sp. and Eustrongylides sp. in the intestine; 3 of acanthocephalans, Acanthosentis cheni, Arhythmacanthus parasiluri and Brentisentis yangtzensis in the intestine and the pyloric caeca. H. lingmueni and A. cheni with rather high prevalence and mean abundance were found in the 3 ecotypes of C. nasus. The marine helminths, such as H. tenuis , E. coiliae and Contracaecum sp. were only found in the anadromous stock, which suggested the 3 helminths can be used as biological tags for discrimination of the anadromous stock. The freshwater helminths, such as S. changjiangensis, A. parasiluri and B. yangtzensis with low infection levels were only found in the freshwater stock, which suggested the 3 parasites can be used as indicator for the freshwater stock. Mean species richness and the Brillouin diversity index were highest in helminth community in the anadromous stock, with higher than 1.25 and 0.19, respectively. Species richness and diversity in the other two stocks were lower than 0.79 and 1.12, respectively. The low diversity in helminth communities of freshwater and landlocked stocks was due to the low infection levels of freshwater parasites and the loss of marine helminths, which was probably caused by the salinity decrease and the absence of the intermediate hosts of marine helminths in freshwater habitat. In addition, geographical isolation could also prevent exchanging of the anchovy and helminths and then lead to decrease of diversity in the landlocked stock.