Examination of the Effects of Dietary Protein and Lipid Levels on Growth and Stress Tolerance of Juvenile Tilapia, Oreochromis niloticus

Tilapia is the second most consumed farmed fish after carp and the most widely grown farmed fish. However, significant price increases in ingredients in recent years threaten profitability of the industry because dietary costs are approximately 60% of production costs. Therefore, the objective of this study was to optimize dietary protein and lipid levels of juvenile tilapia cultured in high‐intensity recirculating‐water system and assess dietary effects on stress tolerance. To achieve this objective, a factorial treatment design with diets formulated to contain three levels of dietary protein (28, 32, and 36%) and three levels of dietary lipid (3, 6, and 9%) was employed. Juvenile tilapia (34.5 ± 0.4 g initial weight) were randomly assigned to each of 24 tanks and fed one of the nine diets, three feedings per day to apparent satiation, 6 d/wk for 12 wk. Fish were weighed and counted every 3 wk and feed consumed recorded weekly. Tilapia weight gain, feed conversion, feed intake, and proximate composition were significantly affected by diet. Following the feeding trial, tilapia were subjected to a 24 h simulated live haul where fish were stocked into a static water system at 0.24 kg/L of water. Glucose, lactate, and cortisol measurements were taken at time 0, 24, and 72 h after fish were placed into hauling containers. There was significant effects (P < 0.05) of crude lipid and crude protein on blood chemistry parameters. These data indicate that practical diet formulations can be improved to enhance growth rates, production of tilapia, and stress response during live hauls.