author(s)
NC Ujjania, LL Sharma and VP Saini

abstract
Environmental conditions of aquatic resources and their suitability play a major role in growth of fishes including non-native species also. Tilapia, (Oreochromis mossambicus) is not a native fish but well adapted to the prevailing local ecological and edaphic conditions of lake Jaisamand, India. The results show that 4 length groups and 4 age classes were observed in the catch which were dominated by large size by length 30-37 cm (67%) and by age 3+ (60%). The dominance of large sized tilapia in the catch is indication of favorability or congeniality of aquatic environment for tilapias in Jaisamand Lake. The growth of fish was inversely related to the age and observed 11.69 cm at 1+ age, 8.67 cm at 2+ age, 7.89 cm at 3+ age and 6.15 cm at 4+ age of fish. It is observed that growth rate of tilapia was better and satisfactory in Jaisamand Lake which is reasoned for efficient use of available food resources by these fishes. The catch composition of tilapia further shows that contribution of tilapia was 0.1% during 1991-92 while it increased up to 98.0% during 2001-02 but declined to 75.0% during 2011-12. This period after 1991-92 represents the invasion and subsequent establishment of tilapias in Jaisamand Lake. Further, the catch composition showed that indigenous fish fauna was adversely affected by such establishment and invasion of tilapia which resulted into a visible decline of age old fisheries of Indian major carps (0.06%), minor carps (0.4%) and catfish (1.0%).