The water quality of rivers is an issue of serious concern today. Rivers are heavily impacted due to their use for carrying off the industrial, municipal, agricultural and domestic effluents. Water samples were collected for the present study from the Ganga River at Kanpur, Allahabad and Varanasi sites, during the period 2011-2012. The minimum temperature (17°C) was recorded in winter season. The pH, TDS, EC, sulphate, phosphate, nitrate, BOD and COD values exhibited their minimum at Allahabad site. The chloride and dissolved oxygen were recorded minimum at Kanpur site while alkalinity and total hardness had their lowest values at Varanasi site. The water quality of the Kanpur site was very poor compared to Varanasi and Allahabad sites. However, the Ganga river waters could host some tolerant fish species such as the exotic Cyprinus carpio and Oreochromis niloticus and also catfishes. All these species are very hardy, in respect of poor water quality, thus they (exotic species) have powerfully invaded in degraded systems worldwide.

Fish assemblages are an important component of aquatic ecosystems. Present investigation was undertaken to study the Persistence, structure and abundance of fishes from the Ganga river (site 1: Kanpur, site 2: Allahabad and site, 3: Varanasi section), India. The Ganga river is a back bone of Indian fishery. The samples were collected monthly during the period June 2011 to May 2013. Canonical correspondence analysis (CCA) indicated that axis 1 and 2 accounted for 67% and 33% variance for species and environmental relation, respectively. Structure of the fish assemblage of the Ganga at Kanupr to Varanasi harbors of 102 fish species belong to 8 orders and 28 families. 74, 89 and 82 fish species were recorded at Kanpur, Allahabad and Varanasi sites, respectively. Cypriniformes and Cyprinidae were the most rich fish species order and family in all sites. At total stretch, Cypriniformes order was shared 49 species, followed by Siluriformes 26 species and Perciformes 17 species. Orders Clupeiformes shared 5 species. Abundance was dominated by Eutropiichthys vacha compared to Clupisoma garua and Sperata seenghala. According to abundance, Cyprinus carpio var. communis (9.64%) and Oreochromis niloticus (9.19%) were powerfully invader in the Ganga river. Exotic species is alarming for indigenous species biodiversity. C. carpio var. communis and O. niloticus are frequently recorded in the Ganga river. Total hardness, alkalinity and dissolved oxygen were responsible for the presence of Catla catla, Rita rita and Sperata aor, while Labeo calbasu, Cyprinus carpio and Cirrhinus mrigala preferred nitrate, phosphate and total dissolved solid for their abundance. Oreochromis niloticus preferred high biological oxygen demand and lead while Zn and Sulphate were responsible for abundance of L. rohita. For conservation point of view C. carpio var. communis and O. niloticus species should be monitored in the Ganga river. Both species are very harmful for fish biodiversity in the Ganga river. Fish assemblage and their abundance know the health of ecosystem.

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Oreochromis niloticus species are adapted to their own set of local ecological and climatic conditions from the Paisuni river, India. Consequently, environmental conditions and their connectivity to organisms may play a big role in generating growth outcome of non-native species in natural conditions. Study was undertaken during the period of October 2015 to September 2016 from the Paisuni river, India. Invasive potential of O. niloticus was measured through size composition, age and growth from the Paisuni river. The total length of fishes varied from 96 to 398 mm with 0+ to 6+ age groups. Their size groups and age groups indicated that the O. niloticus are well stable in the Paisuni river. Their stock and density from the Paisuni river are helping to fisher community for their livelihood and malnutrition as well as poor men malnutrition. The maximum growth increment was observed in 1+ age group (145 mm) and minimum in 6+ age groups (14 mm). The growth of fishes very systematically declined after 1+ age group in the Paisuni river. The maximum fishes were exploited in 241 to 270 mm size group with 18.39%. These sizes of fishes are very attract and magnetize to the fishers from the Paisuni river.

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