Ichthyofaunal diversity in the Gangetic Basin and effect of turbidity on fish behaviour

Gayen, Ipshita (2021) Ichthyofaunal diversity in the Gangetic Basin and effect of turbidity on fish behaviour. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Ipshita Gayen (16MS089)) 16MS089_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

The Gangetic basin supports over 450 million people living in India, Bangladesh and Nepal, and holds record for the most densely populated basin in the world (Payne et al., 2004). Unfortunately, to accommodate the needs of high human density, there has been extensive overfishing causing a decline of many fish species and making it critical to evaluate the current status. Furthermore, the region is dotted with many major metropolitan cities resulting in massive industrial and domestic discharge causing water pollution, which directly affects the freshwater organisms living in the region. Even though multiple government agencies regularly survey the fish population, the data are mostly scattered and lack a systematic statistical analysis. This study addresses the problem by doing a meta-analysis of ichthyofaunal diversity in the Gangetic basin for the last three decades (1990s to present). It will consolidate the scattered data on species occurrence and distribution. This project will help understand how and what environmental and anthropogenic drivers are modifying the ichthyofauna of the world’s most densely populated basin and help policymakers design suitable conservation measures to protect it. The basin is divided into major segments like mountains, plains and floodplains based on topological conditions. We looked at the species distribution patterns down the altitudinal gradient, starting from headwaters in the Himalayas to distributaries draining into the Bay of Bengal. To understand the spatial pattern, we looked into the beta-diversity and split it into its components. It was found that different components are contributing differently to different topological conditions. To understand migration, we looked into the degree of nestedness. Furthermore, we could also find which physicochemical parameters of rivers affect the distribution of the species the most and show that these factors in themselves are affected by the demography and sewage load of the region. Thus indicating chances of indirect anthropogenic effects on species distribution. One of the factors that affect distribution came out to be TDS, which also influences the water systems’ visibility; thus, we are looking into the behavioural changes in the environment with lowered visibility. We found that in wild-caught zebrafish the change in visibility alters the exploration and shoaling tendencies and cause observable difference in sensory behaviour.

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