-This study describes the current status of the small fish community in Niushan Lake in China, and examines the spatial and seasonal variations of the community in relation to key environmental factors. Based on macrophyte cover conditions, the lake was divided into three major habitat types: (1) Potamogeton maackianus habitat, (2) Potamogeton maackianus and Myriophyllum spicatum habitat, and (3) uncovered or less-covered habitat. Fish were sampled quantitatively in the three habitat types by block nets seasonally from September 2002 to August 2003. A total of 10 469 individuals from 27 fish species were caught, among which 20 species were considered as small fishes. Rhodeus ocellatus, Paracheilognathus imberbis, Pseudorasbora parva, Micropercops swinhonis and Cultrichthys erythropterus were recognized as dominant small fishes according to their abundance and occurrence. It was noted that (1) small fishes predominated the total number of fish species in the lake, which reflected to some degree the size diminution phenomenon of fish resources; (2) many small fishes had plant detritus as their food item, which was consistent with the abundance of macrophyte detritus in the lake and implied the importance of detritus in supporting small fish secondary production. Canonical correspondence analysis suggested that the spatial distributions of most small fishes were associated with complex macrophyte cover conditions. Macrophyte biomass was positively correlated with species richness, diversity index and the catch per unit of effort (CPUE) of the fish community. Water depth had no significant effects on species diversity and distribution of the small fishes. Correspondence analysis revealed a higher occurrence of the small fishes and higher abundance of individuals in summer and autumn. Seasonal length-frequency distributions of several species indicated that more larval and juvenile individuals appeared in spring and summer. This study provides some baseline information which will be essential to long-term monitoring of small fish communities in the Yangtze lakes.Key words: Small fishes / Freshwater community structure / Habitat utilization / Multivariate statistics / Lake fishery management / Yangtze lakes Résumé -Structure de la communauté des poissons de petites tailles du lac Niushan connecté au fleuve Yangtze (Chine). Ce travail décrit l'état actuel de la communauté des poissons du lac Niushan (Chine) en examinant la distribution spatiale et les variations saisonnières de la communauté en relation avec les principaux facteurs environnementaux du milieu. Les différentes espèces de macrophytes permettent de diviser les habitats du lac en 3 types : (1) habitat à Potamogeton maackianus, (2) habitat à Potamogeton maackianus et Myriophyllum spicatum, et (3) habitat sans ou peu de macrophyte. Les échantillonnages des poissons des trois types habitats ont été effectués à différentes saisons, de septembre 2002 à août 2003. Au total, 10 469 individus appartenant à 27 espèces de poissons ont été pêchés ; 20 espèces...
Spatial segregation is one of the most important mechanisms that facilitates coexistence among competing species. Large populations of two introduced and congeneric goby species (Rhinogobius giurinus and Rhinogobius cliffordpopei) now co-occur in Lake Erhai, a plateau lake in the Yunnan-Guizhou Plateau (China). Herein we quantified the spatio-temporal distribution of the two species to determine whether spatial segregation occurred within the same ecosystem. A total of 67,819 individuals of R. giurinus and 36,043 of R. cliffordpopei were sampled across four seasons. The results indicated that R. giurinus mostly occupied profundal habitat (PH) while R. cliffordpopei mainly used littoral habitat (LH). Correlation analysis revealed the abundance of R. giurinus was positively associated with deep water, silt and coarse sand substrata, whereas the distribution of R. cliffordpopei was positively associated with high densities of macrozooplanktons and high abundances of other fish species, high concentration of dissolved oxygen and high densities of submerged macrophytes. Except in spring, the body condition of R. giurinus was significantly higher in the PH than in the LH. The body condition of R. cliffordpopei did not differ significantly between habitats in the four seasons. These findings demonstrate that the two congeneric and introduced goby species occupy distinct habitats, indicating that spatial segregation enables coexistence of the two invasive species at high abundances within an ecosystem.
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