The river as transformed by human activities: the rise of the invader potential of Cyprinus carpio and Oreochromis niloticus from the Yamuna River, India.
Cyprinus carpio and Oreochromis niloticus are the most commercially exploited fishes in the Yamuna River, India. Study was undertaken during the period from August 2011 to July 2012 from the lower stretch of the Yamuna River. Analysis of the annual data on fish landing showed that Oreochromis niloticus and Cyprinus carpio have powerfully invaded the site due to poor water quality in the lower stretch of the Yamuna River at Allahabad in a big way. The estimated annual catch was dominated by O. niloticus followed by C. carpio and miscellaneous group as and they contributed for 24.36%, 21.76% and 15.22%, respectively. In case of Indian major carps, Cirrhinus mrigala shared maximum illegible with a contribution of 6.28%. The size composition of C. carpio varied from 10.4 to 69.7 cm while O. niloticus from 10.4-44.5 cm size groups rephrase. The 25.1-30.0 cm size group of C. carpio contributed maximum in the stock (16.03%) and in case of O. niloticus size group 22.1-25.0 cm shared maximum exploitation with 17.05%. The 0+ to 11+ age composition was recorded for C. carpio but in case of O. niloticus only 0+ to 6+ age groups recorded. The urn shaped age pyramid was recorded in both fishes. Unfortunately once C. carpio and O. niloticus establish a breeding population they are extremely difficult to eliminate in the open water. For conservation point of view C. carpio and O. niloticus species should be monitored in the Yamuna River. Both species are very harmful for fish biodiversity and abundance of indigenous fish species in the Yamuna River.