Performance and Muscular Development of Nile Tilapia Larvae (<i>Oreochromis niloticus</i>) Fed Increasing Concentrations of Phenylalanine

Abstract

Even though tilapia is of great economic interest, data on the nutritional requirements of amino acids during commercial breeding stages are scarce. So, the aim of this study was to analyse the performance and muscular growth of Nile tilapia larvae ( Oreochromis niloticus ) fed diets containing increasing concentrations of phenylalanine. The experiment took place at the Laboratory of Aquaculture of the Grupo de Estudos de Manejo na Aquicultura (GEMAq) of the Universidade Estadual do Oeste do Paraná (Unioeste), Toledo, PR, Brazil, for 30 days. A total of 450 larvae, with mean initial length of 1.5 ± 0.14 cm and mean initial weight of 0.04 ± 0.004 g, were randomly distributed into 6 treatment groups with 5 repetitions (30 tanks). Each experimental unit consisted of a 30 L tank containing 15 larvae. Six diets were formulated with increasing concentrations of phenylalanine (1.09, 1.24, 1.39, 1.54, 1.69 and 1.84%) and offered four times a day until apparent satiation. By the end of the experimental period, the following productivity indexes were analysed: length, weight, survival, weight gain, uniformity, feed conversion, specific growth rate and protein efficiency ratio. Three fish from each tank were collected for muscular growth analysis and the frequency of small (<20 μm in diameter) and large (20 - 50 μm) muscle fibres recorded. Small fibres corresponded to 60% - 90% of the fibres observed, suggesting that muscular growth at this stage occurred mainly by hyperplasia. No significant difference (P > 0.05) was observed in the productive performance parameters between the treatment groups. Thus, it can be concluded that the levels of phenylalanine contained in the experimental diets did not influence the performance of Nile tilapia larvae. However, there was more hyperplasia when we put 1.39% of phenylalanine in the diet.