Dietary α-linolenic for juvenile Nile tilapia at cold suboptimal temperature

Abstract

Nile tilapia farming occurs in tropical and subtropical climate areas worldwide but information about dietary fatty acid requirements of Nile tilapia, particularly when raised at suboptimal temperature, are scarce. Previous studies with Nile tilapia failed to detect growth differences at suboptimal growth temperatures. Therefore, the objective of this study was to estimate the dietary requirement of α-linolenic acid (α-LNA, 18:3n−3) of juvenile Nile tilapia, when raised at 22°C. Increasing levels of linseed oil were added to a mixture of vegetable oils, yielding the following concentrations of α-LNA: 0.03, 0.21, 0.37, 0.67 and 0.99% of diet dry weight. The basal diet was formulated with semipurified ingredients and contained 5% lipid. Juvenile tilapia (10.6±0.09g) were fed the experimental diets twice daily until satiation for 14weeks. The average water temperature throughout the experimental period was 22.12±0.17°C. The increase in dietary α-LNA significantly affected daily weight gain, specific growth rate, feed efficiency and daily feed intake. Total n−3 fatty acid content in muscle showed a significant linear response to dietary α-LNA. Likewise, an accumulation of muscle linoleic acid (18:2n−6) was directly related to the increase in dietary α-LNA, while n−6 long-chain polyunsaturated fatty acids (LC-PUFA) decreased. The dietary requirement of α-LNA estimated for juvenile Nile tilapia reared at 22°C was 0.70% diet for maximum weight gain and 0.68% for maximum feed efficiency. Statement relevanceNile tilapia, a tropical species, has been considered for aquaculture in subtropical regions, but its nutritional requirements under suboptimal temperatures are unknown. The present study shows that the α-linolenic requirement for this species under 22°C is slightly higher than in 28°C. Therefore, we suggest the increase in the α-linolenic levels in the diet for Nile tilapia during the cold seasons.