Abstract:

Aim: The Suzhou River, once a typical urban polluted river, flows through the central area of Shanghai. At the end of 1990s, the local government began to carry out the comprehensive treatment of the river environment. The water quality and ecosystem of the river have gradually improved. The purpose of this paper is to evaluate the changes in fish diversity and assemblage during the comprehensive restoration of the Suzhou River in Shanghai in the past two decades.
Methods: The paper sampled 13 sections along the Suzhou River in June (summer) and September (autumn) in 2019. Some statistical methods, such as diversity index, relative importance index (IRI), abundance-biomass comparison curve (ABC curve) and cluster analysis, are used to analyze the characteristic parameters of fish diversity and assemblage.
Results: A total of 10,102 fish samples were collected, comprising 45 species belonging to 8 orders, 15 families, and 37 genera. In summer and autumn, there were 36 species of fish in the upper reaches, 12 and 15 species, respectively, in the lower reaches. From upstream to downstream, the Shannon-Wiener diversity index (H'), the Margalef richness index (D), and the Simpson dominance index (C) showed gradual decreases. Relative importance index (IRI) showed that the common dominant species of the upper reaches in summer and autumn was Pseudobrama simoni, and the lower reaches were Carassius auratus and Misgurnus anguillicaudatus, respectively. The abundance-biomass comparison curve (ABC curve) revealed that the fish assemblage of the whole river was unstable, especially downstream in summer. Cluster analysis and non-metric multidimensional ordination, based on species and quantity, indicated that fish assemblage structure could be divided into two groups, e.g. upstream group I and downstream group II. Pseudobrama simoni, Misgurnus anguillicaudatus, Carassius auratus, Pelteobagrus nitidus and Acheilognathus chankaensis were the main discriminating species causing the differences between the two groups.
Conclusions: Compared with the 43 species in 2001 and 28 species in 2006, the species of fishes showed an increase, especially downstream. This trend of fish migration from upstream to downstream may indicate that water quality differences between the upper reaches and lower reaches is narrowing. The reduction of differences in the fish assemblage between upstream and downstream and the appearances of Culter alburnus, Cultrichthys erythropterus, Abbottina rivularis, and Rhinogobius giurinus in the lower reaches are ecological signs of the comprehensive restoration effects in the Suzhou River.

Key words: Suzhou River, species diversity of fish, assemblage, indicative fish