Evaluation of Nile tilapia strains cultivated in cages under different feeding programmes

The objective of this study was to evaluate the performance of three Nile tilapia Oreochromis niloticus strains cultivated in cages and subjected to different feeding programmes. Initially, 31,200 Nile tilapia juveniles with an average weight of 61.15 g were distributed in 48 cages. Two genetically improved strains were used together with one from the Fish Culture Section of Universidade Federal de Lavras (UFLA). The fish were subjected to four feeding programmes, consisting of different levels of crude protein (CP) in diets provided at different stages of cultivation. There was no interaction effect of the strain and feeding programme for most variables. The UFLA strain presented the highest weight gain, but with greatest lack of uniformity at the end of cultivation. The feeding programme with diets containing 36%, 32% and 28% CP, consecutively, promoted the highest weight gain and highest final biomass. The UFLA strain has great growth potential, justifying the development of a breeding programme for this strain. Crude protein levels below 36% for tilapias between 60 and 170 g and below 32% for tilapias between 170 and 700 g worsen fish performance.