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The River Tamas is a right-bank tributary of the River Ganga flowing through the states of Madhya Pradesh and Uttar Pradesh, India. It originates in Jhukehi village in the Satna district of Madhya Pradesh and after 268 km it joins with the River Ganga at Sirsa, Prayagraj, Uttar Pradesh. The river has a diverse habitat and harbours a variety of flora and fauna. More than 70 fish species reside in the river, along with other biotic communities. A barrage, named Tons and situated at Bakiya village, was commissioned in 1992 for hydro-electric purposes. The continuity and volume of water in the river have been disturbed due to the construction of this barrage and it has changed the ecology and biodiversity. Keeping the ecosystem intact requires that environmental flow calculations be made of the river at the barrage. An attempt has been made to estimate the environmental flow requirement using a desktop hydrological method. Based on the flow duration curve (a hydrological method of flow estimation), the environmental flow for the River Tamas has been calculated using Global Environmental Flow Calculator software. Our calculation are based on flow discharge data received from the Tons Barrage Authority at Bakiya for the period January 2006 to December 2017. Average annual discharge was calculated from the recorded maximum (151.46 cumecs in 2016) and the minimum, 13.53 cumecs in 2007. Mean Annual Runoff was calculated as 1607 Million Cubic Meter with Coefficient of Variation =0.799. To maintain the river in the “slightly modified” class of Environmental Management Class, 27.8 % of Mean Annual Runoff discharge should be released into the river to largely maintain the biodiversity and habitat, while about 57% of Mean Annual Runoff discharge is required to maintain this river in pristine condition. This is a preliminary study to determine the water requirements for healthy habitat and biodiversity of the Tamas river.

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.

The understanding of patterns in fish assemblages is imperative for management and conservation plans. There is a dearth of information on the environmental factors affecting the fish community structure in the reservoirs built on the intermittent rivers of India. We hypothesized that the environmental factors most likely influenced the patterns in the structure of fish diversity at temporal and spatial scales in a sub-tropical reservoir of the Ganga River basin. The data was gathered seasonally from April 2017 to March 2018 from three sites each in the riverine, transitional, and lacustrine zones of the reservoir. About 16,220 fish specimens were captured that belonged to 7 orders, 14 families, 31 genera, and 40 species. The diversity indices showed the highest diversity in the riverine and the lowest in the lacustrine zones of the reservoir. At a temporal scale, the highest diversity was observed in the monsoon season and lowest during the summer season. The cluster analysis spatially separated the fish fauna into three groups, each group formed by sampling sites in the riverine, transitional and lacustrine regions of the reservoir and may have resulted from physico-chemical and anthropogenic influences. Our study suggests the need to consider the possible influence of altered environmental conditions on fish assemblage, and some recommendations were suggested for the improvement of the fisheries impacted by the construction of dams.