Invasion of an Exotic Fish—Common Carp, <I>Cyprinus Carpio</I> L. (Actinopterygii: Cypriniformes: Cyprinidae) in the Ganga River, India and its Impacts

Abstract

Background. The Ganga River (Ganges) is known of its rich fish diversity which is adversely affected by degrading environmental and ecological conditions. There are more than 300 exotic fish species in India. Many of them (particularly Cyprinus carpio) escaped from confinement and are now present in the Ganga River, chal- lenging its ecological equilibrium. The aim of this project was to study the population characteristics of Cyprinus carpio (i.e., the abundance, s ize range, food and feeding, gonado-somatic index (GSI), gonad maturity stage, maturity and breeding) and the altered fishery dynamics. Materials and Methods.The commercially caught fishes, including the exotic ones, were identified, examined and measured. Important indices such as: the abundance index of exotic fishes, the gonado-somatic index (IG), as well as the gonad maturity stage of the escapee C. carpiowere determined. The gut content was also analyzed t o identify food items and thereafter the food richness, diet breadth, and gut repletion index (GRI%) were calcu- lated using the Simpson's diversity index. Results. C. carpiointroduced about sixty years ago for aquaculture has now been found to invade into the Ganga, the largest river of the country contributing significantly to the fishery. The abundance index of C. carpioranged from 12.2% to 45.5 % in 250 km long river stretch of the Ganga River flowing along Kanpur t o Varanasi in the state of Uttar Pradesh. The gut content analysis revealed the presence of Eichhornia (9.8%), Pistia (11.6%), Nymphaea(8.5%), annelids worms (7.8%), algae (20.2%), mud and detritus (14.8%). The calculated diet breadth ranged from 0.82% to 0.91%; food richness ranged from 12 to 16, and the gut repletion index (GRI%) was 100% at different sampling sites. Mature females represented all the six reproductive stages with varying gonado- somatic index (IG) (0.5 to 30) in different catches. Presence of spent, ripe, and mature females was recorded. Conclusion.Abundance of exotic fish primarily C. carpioand Oreochromis niloticusin the fishery of the Ganga River was observed. The gonado-somatic index (IG) and the presence of all the six gonadal stages confirmed that C. carpio established its breeding population. The dominant catch of exotic fishes negatively impacted on the important indigenous fishes particularly Indian m ajor carps (Catla catla, Labeo rohita, and Cirrhinus mrigala). The change in dynamics of the fishery due to the presence of common carp attracted attention to conserve rich indigenous germplasm facing threats of shifting from their natural habitats.