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Temporal and spatial variation in fish assemblages in Lake Taihu, China

Set-net surveys were performed monthly between January 2010 and December 2012 at six sampling sites in Lake Taihu in order to determine the spatial and temporal variation in fish assemblages in Lake Taihu and to assess the influence on fish assemblages of eutrophication and disconnection of migration routes. A total of 134,604 specimens (1456.7 kg total biomass) were caught, representing 61 species, 18 families, and 10 orders. Cyprinidae fish (36 species) contributed most of the total species richness and the most dominant species was Coilia nasus. Sampling months and sampling sites each significantly affected the Margalef richness index, Shannon–Wiener diversity index (H′), and Piélou's evenness index (J′) of fish assemblages and there were interactive effects between them. The ANOSIM analysis indicated that the fish assemblage structure had significant differences among the sample sites. Total nitrogen (TN) and total phosphorus (TP) both differed significantly among sites. The results of correlation analyses suggested that there was a significant negative correlation between two indices (H′ and J′) and both TP and TN (p < 0.01) as well as a significant positive correlation of catch per unit effort with both TP and TN (p < 0.01). Our results suggest that eutrophication in Lake Taihu has led to an increase in small-sized phytoplanktivorous and zooplanktivorous fishes and a decrease in prey availability for predatory fishes. Thus, the relative importance of small-sized fishes has increased and a few small-sized species (e.g., C. nasus) have become the dominant species, as reflected by reductions in the species diversity indices (H′ and J′).