Seasonal dynamics and distribution of the digenean Phyllodistomum pawlovskii (Trematoda : Gorgoderidae) in the bullhead catfish, Pseudobagrus fulvidraco, in a lake of China

Seasonal population dynamics of the digenean Phyllodistomum pawlovskii in the urinary bladder of the bullhead catfish, Pseudobagrus fulvidraco, were investigated in Liangzi Lake in the flood plain of the Yangtze River in China from February 2001 to July 2002. The overall prevalence of the parasite was high, 41.5% (n = 1,476), while the mean abundance was relatively low, 1.24 +/- 2.11. The parasite exhibited evident seasonality in changes of prevalence and abundance. In brief, prevalence and abundance were very low in midwinter (January), but increased and remained relatively high in other seasons and months. The distribution pattern of this parasite in the fish was overdispersed, with a variance to mean ratio > 1, but its frequency distribution could not be described by the negative binomial model. There were positive correlations between the number of the parasites per fish and the age and length of the fish; a peaked age-parasite abundance curve was not detected in the parasite-host association. It is suggested that the parasite P. pawlovskii has little effect on the population structure of the bullhead catfish.

Observations on two species of phyllodistomes (Trematoda : Gorgoderidae) from fishes of the Hubei Province, central China, with an erection of Neophyllodistomum gen. n.

Two rare trematode species so far reported in the genus Phyllodistomum Braun, 1899, P. pawlovskii (Zmeev, 1936) and P. serrispatula Chin, 1963, were found in the urinary system the yellow catfish Pelteobagrus fulvidraco (Richardson) of Bao'an Lake (prevalence 8 %) and the swamp eel Monopterus albus (Zouiev) of Liangzi Lake (prevalence 6 9/6), respectively, from the Hubei Province, central China. In contrast to the original description, P. pawlovskii showed a considerable morphological variability particularly in the shape, size and topography of testes. A unique morphological feature of P. serrispatula is the presence of many conspicuous lateral outgrowths on the hindbody and, principally based on this character, a new genus Neophyl-lodistomum is erected (type species N. serrispatula (Chin, 1963) comb. n.)) to accommodate this species. Both trematode species are briefly redescribed. P. pawlovskii and N. serrispatula are reported for the first time from the Hubei Province and the former from the Yangtze River drainage system.