9.3.3.5 Uncontrolled introduction of exotic fishes

9.3.3.5 Uncontrolled introduction of exotic Fishes

Many foreign species have been introduced in Indian waters and some are now well-established too. They include Salmo salar, Salmo trutta fario, Oncorhynchus mykiss, Oncorhlynchus nerka, Salvelinus fontinalis, Cyprinus carpio, Carassius carasius, C. auratus, Oreochromis mossambicus, Ctenopharyngodon idella, Hypophthallmichthys molitrix, Tinca tinca, Osphronemus goramy, Gambussia affinis, Lebestes recticulatus, Clarias affinis, C. garipinus and Pygocentris nattereri.

Introduction of exotic fast-growing species is causing threat to our indigenous fish diversity. Common carp introduced into Kashmir valley has almost exterminated the indigenous schizothoracids. Similarly, Osteobrama belangeri, the endemic fish to Loktok Lake is disappearing fast due to the introduction of common carp. In Gobindsagar dam, the Indian major carp, especially Catla, has already been replaced by the silver carp recorded that the establishment of Cyprinus carpio and Hypophthalmichthys molitrix have alarmingly declined the mahseer (Tor putitora) fishery in Govindsagar reservoir. Rercently, Sugunan has emphasized that all the three varieties of common crap, viz Cyprinus carpio communis, C. carpio specularis and C. carpio nudus are not suitable for stocking in most of the Indian reservoirs as they are vulnerable to predators and are seldom caught in passive gears. Besides, they compete with indigenous species like Cirrhinus spp, snowtrout and Osteobrama belangeri. The recent capture of Hypophthalmichthys molitrix, Ctenopharyngodon idella and Cyprinus carpio in Yamuna and Gomati rivers of Uttar Pradesh is causing concen.

The tilapia, Oreochromis mossambicus, introduced accidently into some South Indian reservoirs like Amaravati and Vaigai, has firmly established itself and has completely replaced the endemic fauna. Similarly, Gambussia spp. practically ousted all indigenous fish fauna of Ooty lake at one time. Sugunan (1994) has remarked that the three exotic species like Cirrhinus molitrorella, Molypharyn godon piceus and Hypophthalmichthys nobilis, being considered for introduction, are reported to be unsuitable. There are apprehensions that Clarias gariepinus may be adversely affecting our indigenous Clarias batrachus.

The introduction of trouts in almost virigin niche at high altitude coldwater streams have, however, remained encouraging in India. Some exotic food fishes have also been performing well by enhancing production in closed culture system. Sugunan suggested that Oreochromis niloticus which grows to 250 g in 6 months and its prolific breeding may probably be more suitable for Indian reservoirs. However, Dehadrai has remarked that the introduction and transfer of exotic species for aquaculture purposes may change or impoverish the biodiversity and genetic resources through inter-breeding, competition for food, habitat destruction and possibly through transmission of diseases.

Last modified: Thursday, 1 December 2011, 1:27 AM