Ichthyofaunal integrity and environmental features trade-off in the Sundarbans, India

Herein, we studied the ichthyofaunal diversity of the Bidyadhari River in the Indian Sundarbans for three consecutive months (April 2018-June 2018). The fishes collected in this study were netted from two collection points using bag nets. We also measured some environmental parameters during the time of netting. From the collection, we determined the Simpson's index of diversity (1-D), the Shannon-Wiener index (H), evenness (E) and the Sorenson's coefficient of community (CC) to find out the species richness, abundance, evenness and the levels of similarity of the two collection points. We also converted the H values to their true diversities (effective number of species [ENS]) for an adequate comparison. The indices and coefficient (H = 3.72-3.94, E = 0.830-0.832, 1-D = 0.973-0.979 and CC = 0.87) indicate that the overall integrity of biodiversity of the two collecting points is high. From the true diversity values, we ascertained that the first point, having 62 species of fishes, is 1.24 times as diverse as the second one, having 50 species. We have attributed the fish diversity to a compound of abiotic and biotic factors, which we explain in the discussion part. We also documented 20 fish species, new records for the Indian Sundarbans; some are new records from West Bengal. Furthermore, we discuss the possible reasons for their occurrence. Our study brings the number of fish species recorded from the Indian Sundarbans to 378.