Ecology Of Endohelminths In The Yellowhead Catfish, Pelteobagrus Fulvidraco

The yellowhead catfish Pelteobagrus fulvidraco (Richardson) is widely distributed in rivers and lakes in China, and has become an important species for aquaculture in China. The present study aims to investigate the ecology of populations and communities of endohelminths in alimentary tract and urinary bladder of P. fulvidraco in lakes in the flood-plain of middle reaches of the Yangtze River. Population dynamics and frequency distribution of seven species of helminths were studied from February 2001 to July 2002 in P. fulvidraco in Liangzi Lake in Hubei province. The nematode Procamallanus fulvidraconis exhibited obvious seasonality in changes of abundance, but not in prevalence. The number of mature females of P. fulvidraconis without eggs reached high level in February and March, the number of those with eggs was high in May and July, and gravid females with larvae inside were observed in a relatively high level from June to September. Significant changes were found in prevalence and abundance in the cestode Gangesia pseudobagri. An obvious pattern of seasonal fluctuation was also observed in prevalence and abundance of five species of digeneans, i.e. Genarches goppo, Orientocreadium siluri, Coitocaecum piageorchis, Echinoparyphium lingulatum and Phyllodistomum pawlovskii except for the prevalence of O. siluri. In addition, factors influencing the seasonal occurrence, such as water temperature and life cycle of parasites were discussed. The community structure of intestinal helminths of the yellowhead catfish was compared among the 2 Yangtze River-connected and 5 river-isolated lakes. The species richness was all high in these communities, and not significantly correlated with the area of lakes. The infra-communities exhibited the nested assemblage. The communities in these lakes showed high degree of similarity. It is thus indicated that the recent river-lake isolation in the flood-plain lakes of middle reaches of Yangtze River had no detectable effect on the community structure of intestinal helminthes of P. fulvidraco. The similarity in the composition of the helminth communities may be to a large extent due to the similar limnological characteristics in these lakes. To investigate whether recent habitat fragmentation affected genetic divergence of populations of the nematode P. fulvidraconis in the yellowhead catfish P. fulvidraco at a macro-and micro-geographic scale. Twelve populations of the nematode were collected from 12 localities in 7 flood-plain lakes. Genetic variation was observed mainly within populations and the genetic diversity within populations was much higher than among populations both at large and small scales using 11 ISSR markers. Significant difference was not observed in the genetic diversity of P. fulvidraconis between river-connected and isolated lakes. Population subdivision among populations at large scale was significantly higher than at small scale. Test for isolation-by-distance revealed the significant positive correlation between geographic and genetic distance. The undetectable effect of fragmentation of river-lake complex ecosystem on genetic diversity of the nematode populations may be due to the fact that the river-lake isolation is indeed a recent process, and may also to the flood of the Yangtze River as flooding water may cause the spreading of the nematode. The nematode may also be transmitted by the transportation of the yellowhead catfish and other species of fish which can serve as its definitive hosts. However, it may also be possible that the population size of the nematode in these lakes is bigger enough to maintain its population structure. In addition, helminth parasites were investigated in fish in Lhasa River in Tibet, China. A total of 11 parasite species were found, including Allocreadium spp.,Breviscolex orientalis, Ligula sp., Diphyllobothrium sp., Rhabdochona hellichi, Contracaecum sp., Eustrongylides sp. Neoechinorhynchus qinghaiensis, Echinorhynchus gymnocyprii and an unnamed acanthocephalan. The prevalence and mean abundance of each parasite species were calculated.