OPTIMAL DIETARY-PROTEIN CONCENTRATION FOR HYBRID TILAPIA OREOCHROMIS-NILOTICUS X OREOCHROMIS-AUREUS FED ALL-PLANT DIETS

There are several estimates of the optimal dietary crude protein conce ntration for juvenile tilapia fed high quality animal proteins or mixt ures of animal and plant derived feedstuffs. In the present study, the optimal dietary crude protein concentration for hybrid tilapia Oreoch romis niloticus x O. aureus reared in glass aquaria was determined usi ng diets free of fish meal. Further, initial weight of fish was approx imately 21 g, which is the beginning of the growout phase of many comm ercial operations. The diets contained primarily corn coproducts and s oybean meal as the sources of amino acids, and were formulated to prov ide 24, 26, 28, 30, 32 or 34% crude protein. The diets were fed to qua druplicate groups of tilapia for 10 wk. Increasing concentrations of d ietary crude protein resulted in proportional improvements in weight g ain and feed efficiency up to 30% dietary crude protein. Fish fed 24% dietary crude protein exhibited significantly reduced weight gain comp ared to fish fed 28-34% dietary crude protein. Protein efficiency rati o (PER) of tilapia was unaffected by dietary crude protein concentrati on. However, fish fed 28% crude protein exhibited numerically higher P ER (2.58) than fish fed other levels of crude protein. Muscle crude pr otein levels were lower in fish fed diets containing 24-28% crude prot ein than in fish fed 30% and higher concentrations. Quadratic regressi on analyses of weight gain and feed efficiency data indicated the opti mal dietary crude protein concentration to be 29.65% and 28.33%, respe ctively, while broken line analyses indicated 27.5 and 27.3%, respecti vely. Based on weight gain, feed efficiency, PER, and proximate compos ition data, the authors recommend 28% dietary crude protein as the min imum for hybrid tilapia fed all-plant diets and reared in tanks.