Effects of size grading and large individuals on growing performance of hybrid Tilapia (O. niloticus × O. aureus) fry

The aim of this study is to investigate the effects of size grading and large individuals on the growing performance of small individuals of hybrid tilapia fry produced by crossbreeding broodstock of Oreochromis niloticus? and Oreochromis aureus?. The 0 age 1.00 g hybrid fry which have not completed the larval period were stocked as 50 fry/m³ in 1 m³ cages placed in a pond and cultured for 60 days. The test group comprises three groups, one graded group consisting of only small individuals and two mixed groups consisting of 50% and 75% small individuals respectively. After the trial it was observed that the growing of the graded group (26.36±0.51g) is better than the small individuals of the mixed groups. The daily average weight gain (0.42±0.01g/day), specific growth ratio (5.45±0.03 %/day) and porportional weight increase (2537.86±48.23%) of the graded group were found to be higher than the small individuals of the mixed groups. The food conversion ratio of the three groups were similar to each other (p<0.05). It was determined that the size grading has no effect on feed conversion ratio. Consequently it was observed that size grading has a positive effect on growing performance of hybrid tilapia fry in cage culture condition.