*, Mehraj Din Bhat 1

Oreochromis mossambicus (Peters, 1852) is a highly successful invader of aquatic ecosystems due to its adaptable life history, tropic flexibility, ability to tolerate extreme and often unfavourable environmental conditions, rapid reproduction and maternal care of offsprings. Upon introduction to areas outside its natural range, these characteristics often give O. mossambicus a competitive advantage over indigenous fishes. The present study investigated the population characteristics of non-indigenous Mossambique Tilapia, O. mossambicus, for a period of 12-months from August 2009 to July 2010 in the lower stretch of Yamuna River in India. The Mossambique Tilapia, O. mossambicus, formed the most abundant fish species in all the catches from the Yamuna River at all the sampling stations. The gonado-somatic index (GSI) and the presence of all six gonadal stages confirmed that O. mossambicus has established a breeding population. The GSI for females indicated year-round reproduction with increased spawning intensity in spring (March to April) and monsoon (July to August). Males ranged from 142-280.0 mm total length (TL) and females from 130-265.0 mm TL. Small juvenile fish were collected every month of the year and multiple size classes present in sampling catches suggest successful recruitment of young. Adult O. mossambicus consumed primarily detritus and vegetal matter, though the diet of juveniles, collected from the Yamuna River, was found to b