Revealing the temporal dynamics of fish assemblage pattern, feeding guilds in relation to habitat quality parameters in a coastal wetland of the Indian Sundarban eco-region

The present study was conducted from April 2016 to March 2017 in a freshwater-dominated coastal wetland of the Indian Sundarban ecoregion to illustrate the fish diversity, and abundance and the predictor variables determining fish assemblage structure in the wetland. A total of 27 fish species belonging to 13 orders, 16 families, and 23 genera with Cyprinidae (18.5%) as the most dominant family were recorded from the wetland. Fish species richness was found to vary noticeably across the season with the highest number of taxa during the monsoon season (25 species). The study revealed that small indigenous fish species (SIFs) were found dominating the overall species richness and abundance which accounted for 70.37% of the total fish diversity. Among SIFs, Mystus gulio dominated (33 - 42%) the total fish abundance followed by Amblypharyngodon mola (12 - 21.7%), Oryzias dancena (11 - 14.9%), Parambassis ranga (6 - 32%), Puntius sophore (5 - 10.8%), and Parambassis lala (3 - 5.9%). Thirteen fish species were found as inhabitants of truly freshwater, eight species of freshwater and brackish water, and six of freshwater, brackish, and marine form. The developed GAM model proved water turbidity to be the best predictor variable determining fish abundance and assemblages in the wetlands. Besides, turbidity, salinity, transparency, and temperature were found to influence the fish assemblages. There was no visible response to water depth, although this has a linear effect on fish abundance. Water temperatures up to about 30.5 °C had a positive effect on fish abundance and the highest fish abundance in the wetland to be found in the range of 29 to 30.5 °C.