AGroup of the exotic crayfish, Procambarus clarkii (total length ranging from 4 to 6.1 cm) was held with the early stages of fry of common carp, Cyprinus carpio Linnaeus, 1758 ; silver carp, Hypophthalmichthys molitrix (Valenciennes, 1844) ; Nile tilapia, Ore'ochromis nihticus (Linnaeus, 1757) ; and Sartherodon galilaeus (Artedi,1757), with initial average lengtii ranging from 2 to 2.5 cm and fingerlings with initial average length rangmg from 4.1 to 5.8 cm . Each species were held separetely with the crayfish 5 aiming to find out its effect on both survival and growth rates of the above fin fish in polyculture.The results indicated that the survival rates ranged from 74.4 to 88.9% compared with a range of 76.6 to 94.65% in control experiments for the early fry stages of the four different fish species. For the fingerlings the range was 71.1 to 93.3% compared with 76.65 to 93.35 % in control experiments .There were no significant differences in the survival rate of the four fish species cultured in combination with the crayfish and the fish kept alone ( control).
When rearing O. niloticus ( 2.3 g in weight and 4 cm in length ) with young crayfish ( 1.76 g in weight and 4.39 cm in total length ) for three months, the results showed that the final weight was significantly different (P < 0.01 ) for fish reared alone, while no significant differences were observed in weight gain and specific growth rate. There was, however, a significant difference ( P< 0.001 ) in the final weight for crayfish reared in combination with tilapia, while there were no significant differences in weight gain or specific growth rate. It seems that the presence of crayfish in a mixed culture