Exploitation is an economic activity governed by social needs and pressures. Freshwater fishing is a major source of income and protein for the riverine populations of most tropical regions. Labeo calbasu is a herbivores and bottom feeder fish. It is distributed throughout India, Pakistan, Bangladesh, Burma and Nepal. It is economically important fish species in the Yamuna river and supports an important commercial fishery in rivers, reservoirs, lakes and even in ponds. During study period 176 specimens of L. calbasu were collected from the lower stretch of the Yamuna river at Allahabad, Uttar Pradesh. Size composition varied from 11.2 to 52.0 cm size group and indicated that the stock of L. calbasu in the river was in healthy condition. 32.1-35.0 cm size group was dominated (17.61%) compared to 29.1-32.0 (13.64%) and 26.1-29.0 cm (11.93%) in exploited population. Middle size group was maximum exploited at Allahabad. Higher size group shared minute proportion in exploited population. The exploitation pattern was not systematic in lower size group. Current exploitation pattern is alarming for future. Data also indicated that the fishing activities should be prohibited in breeding season.

Pen culture for in situ raising of stocking material was conducted in Sareni Jheel, located in the Rae Bareli District of Uttar Pradesh. Sareni Jheel, being rich in organic carbon (4.5%) and nutrients, higher values of silt (29%) and clay (15%) were recorded. Rich oxygen levels, alkaline pH, high organic matter, moderate to high chemical parameters suggested moderately productive nature of this wetland. Pen with high-density polyethylene (HDPE) net was installed in an area of 0.1378 ha and stocked with advanced fry of the Indian major carps, rohu Labeo rohita and catla Catla catla in the ratio of 1:1 @ 25 nos. m-2. No significant changes in water quality parameters were noticed within and outside the installed pen. Mean weight at stocking of rohu and catla was 2.88±1.41 g and 2.1±1.16 g, which increased to 57.2±13.84 g and 67.38±25.79 g respectively, in 120 days. The average feed conversion ratio (FCR) recorded was 1.08 with overall survivability of 69.52% in rohu and 74.74% in catla. Benefit-cost ratio and return on investment were calculated as 1.69 and 0.69, respectively. Intervention through pen culture resulted in the increase in fish productivity of Sareni Jheel from 310 to 833 kg ha-1.

The Ken and Betwa rivers traversing through Central India are the major tributaries of the river Yamuna. Both rivers originate above 550 m above sea level in the Vindhya region. An interlinking project proposed for the rivers envisages diversion of water from Ken basin to the Betwa. The river sediment is alkaline and dominated by sand (78–89%) in both rivers. Oxygen-rich alkaline water and moderate values of chemical parameters show the pollution free and productive nature of both the rivers. There was no statistically significant difference in water quality between the Ken and Betwa rivers, except for total alkalinity. The biotic parameters were observed in similar ranges and moderate condition. A total of 61 planktonic forms were recorded from the rivers out of which 55 were phytoplankton. For the first time, 89 fish species belonging to 10 orders, 26 families, and 62 genera have been recorded in the river Ken, while 81 species classified under 10 orders, 24 families, and 55 genera were found in the Betwa. Exotic fish species were also observed in the downstream stretches of both rivers. Out of the total fish species, 77 were common to both rivers, 12 were found only in the Ken River, and 4 species were restricted to the Betwa. Analysis of relative abundance showed dominance of Labeo boggut in the Ken and Osteobrama cotio in the Betwa River. On comparison of the Shannon–Wiener Diversity and Evenness Indices of fish diversity, these indicated slightly higher values in the Ken (3.76 and 0.842) than the Betwa (3.66 and 0.835). A total of nine near-threatened fish species was recorded in the rivers. Both rivers have already been obstructed by many developmental projects; the proposed interlinking would further negatively impact the ecology and fisheries.

The relationship between length and weight of three fish species Johnius coitor (Family Sciaenidae), Osteobrama cotio (Family Cyprinidae) and Gonialosa manmina (Family Clupeidae) unknown to Fishbase were studied from the Allahabad waters of the river Ganga in India. Fishes were captured bi‐monthly from March 2017 to June 2018 using gill nets and cast nets of various mesh sizes. The b values determined from length‐weight relationships (LWRs) were 3.246, 3.373 and 3.024 for J. coitor, O. cotio and G. manmina, respectively.

The river Ganga originates from Gangotri and travels approximate 1,300 km to Vindhyachal, bypassing through a series of dams. Water quality parameters including temperature, pH, dissolved oxygen, alkalinity, chloride, biological oxygen demand, dissolved organic matter, and nutrients were studied from various centers of the river Ganga from Gangotri to Vindhyachal (24 centers). Specific conductivity increased gradually from Maneri above barrage area and reached maximum at Kanpur as the river receives industrial and domestic effluents near Kanpur. Allahabad, Haridwar, and Vindhyachal sampling points were found to be affected by anthropogenic influences. A chloride as well as Myxophyceae were maximum at Kanpur, which indicated that maximum organic pollution at Kanpur plankton population and composition were much more affected by temperature and nutrients than by the construction of dams. However, the pattern of release of water affected the accumulation of nutrients in surface water, which impacted the quality of planktonic fauna and flora. The upper stretch was dominated by diatoms and the middle stretch by green and blue‐green algae as the accumulation of nutrients exhibited eutrophic conditions. Near the source, diatoms like Eunotia, Achanthes, Cymbella, Diatoma, Tabellaria were found to be dominant but as river moves toward downstream, species of Synedra, Melosira, Nitzchia, and Cyclotella became abundant. The study revealed how water quality deteriorated by the construction of each dam. Therefore, when making policy for a dam on any river it is important to maintain at least one stream of the original water flow. The whole river should not be blocked at any point/place or at least 50% of original water should flow continuously to sustain the biodiversity and quality of water, otherwise after traveling a few kilometers through dams, a river will lose its originality.