Fish assemblage pattern, seasonality and their interaction with environmental variables: insights from canals of Sundarbans, India

Abstract

In the present study, the fish distribution and assemblage pattern in relation to environmental variables were studied in the canals of Indian Sundarbans. The Permutational analysis of variance (PERMANOVA) depicted the significant variation of water variables between the seasons (F = 10.40; p = 0.001), and stations (F = 1.96; p = 0.011). A total of 44 species belonging to 39 genera, 30 families and 16 orders were recorded with Cyprinidae (6 species) as the apex contributor. Significant temporal variations of fish Species Richness per sample (SRp) (p ? 0.05) were observed between pre-monsoon and monsoon season. By and large, fish assemblages did not portray the significant seasonal variation hinted towards the limited connectivity with tidal water through the sluice gate, thereby minimizing the movement of fish species between the canal and river. The fish assemblages pattern exhibited an overall 30% similarity among all the stations. The calculated value of Margalef richness (d?) and Shannon diversity (H?) indices (4.42 ? 0.84 and 2.62 ? 0.18 for d? and H?, respectively) indicating a moderate fish diversity in the canal system. The water variables such as temperature, dissolved oxygen, pH, salinity, specific conductivity, transparency, depth and water flow play important role in structuring the fish assemblages in the studied canals which were evident from the BIO-ENV module, and the distance-based redundancy analysis (db-RDA). Meagre seasonal variation of fish populations related to variations in species-specific adaptation to the prevalent ecological conditions.