Fish diversity, community structure, and environmental variables of River Tamas, a tributary of River Ganga, India

The Tamas River is a right-bank tributary of the River Ganga, originating from Jhukehi village in Madhya Pradesh and meeting up with the Ganga at Sirsa, Prayagraj, Uttar Pradesh, India. An investigation was carried out in six sites at (Itahara, S1), (Madhavgarh, S2), (Bakiya upstream, S3), (Bakiya downstream, S4), (Chakghat, S5) and (Panasaghat, S6) of the river to document the fish diversity, seasonal variability, and impact of environmental variables on fish species composition during the period 2017 to 2019. Altogether 75 fish species belonging to 54 genera, 23 families, and 10 orders were recorded. Fish species richness at (S1), (S2), (S3), (S4), (S5), and (S6) and was recorded as 9, 39, 38, 13, 61, and 49, respectively. Family Cyprinidae with 31 species contributing 41% was the most dominant family, followed by Bagridae (8%) and Schilbeidae (6.7%). Seasonal variation in fish species richness and diversity indices were observed in the river stretch. Maximum species richness (45) was observed at S5 during monsoon and a minimum (6) at S1 during post-monsoon. As per the International Union for Conservation of Nature categorization, 10 out of 75 fish species recorded from the river were considered to be threatened. Three exotic species, namely Cyprinus carpio, Oreochromis niloticus, and Hypophthalmichthys nobilis, were recorded at some stretches, which may be a concern for native fish diversity. Environmental variables like water temperature, pH, dissolved oxygen, water velocity, and alkalinity influenced the fish community structure. The selected (S1-S6) stretch of the river falls under the category of Slightly Impacted River based on the Shannon Index (H'>3). The present investigation was the first assessment of rich fish diversity covering the maximum stretch of river, which supports many important and small indigenous fishes for conservation.