Examination of the effects of dietary protein and lipid on growth and stress response of Nile tilapia cultured in high intensity systems
Hooley, Christopher Gary
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Tilapia is the second most consumed farmed fish, after carp, and the most widely grown of any farmed fish. Significant feed price increases in recent years threaten sustainability of the industry. In the US tilapia are often subjected to extended hauling to reach live-fish markets. Therefore, the objectives of the current study were to optimize dietary protein and lipid levels for juvenile tilapia cultured in high-intensity recirculating-water system and assess how dietary changes alter hauling stress-tolerance. To achieve these objectives, a 3 X 3 factorial design was used with practical-type diets formulated to contain three levels of dietary protein (28, 32 and 36%) and three levels of dietary lipid (3, 6, and 9%). Juvenile tilapia (34.5 ± 0 .4g initial weight) were fed one of the nine diets, three feedings/d to apparent satiation, six d/wk for 12wk. Fish were weighed and counted every three weeks and feed consumed recorded weekly. At the conclusion of the feeding trial, three fish per tank were sampled for proximate composition analyses. One week post-conclusion of the feeding trial, tilapia remaining in each tank were subjected to a simulated live haul in which fish were transferred to insulated container (2lbs/gallon) with supplemental oxygen for 24h, and then returned to their source tank and allowed to recover for an additional 48h. Hematocrit, glucose, lactate and cortisol measurements were collected at time 0, 24h, and 72h. Increasing dietary protein significantly improved tilapia weight gain (P=0.01), feed conversion (FCR, P=0.03), feed intake (P=0.02), protein retention (P=0.01) and filet ratio (P=0.01). Increasing dietary lipid also significantly improved weight gain (P=0.05) and FCR (P=0.01) but at 9% decreased feed intake (P=0.02). Blood chemistry values were also altered by dietary protein and lipid levels (Figure 1). No significant interactions between dietary protein and lipid levels on growth performance or blood chemistry values were measured. Results of this study suggest that while increasing protein and lipid levels in tilapia diet formulations improved production of tilapia cultured in high intensity systems and that, stress tolerance during live hauls appeared to be reduced.