Dietary supplementation of Aurantiochytrium sp. meal, a docosahexaenoic-acid source, promotes growth of Nile tilapia at a suboptimal low temperature

Abstract

Information regarding the fatty-acid requirements of Nile tilapia raised in cold-suboptimal temperatures is scarce. Ectothermic animals, such as tilapia, tend to increase the degree of unsaturation in their membrane fatty-acids in cold temperatures to maintain cell membrane function. Therefore, we fed Nile tilapia juveniles (8.47 ± 0.19 g) at a cold suboptimal temperature of 22 °C, with four different supplement concentrations of Aurantiochytrium sp. meal (0.5, 1.0, 2.0, and 4.0 g 100 g−1 dry diet), a source of docosahexaenoic acid (22:6 n-3, DHA), to assess its effect on growth, nutrient retention, and digestibility. We also included a positive control diet with cod liver oil (CLO), containing a DHA concentration similar to the diet supplemented with 1.0 g 100 g−1Aurantiochytrium sp. meal, to allow for a comparison of two DHA-rich food sources. Fish were fed the experimental diets twice a day to apparent satiation for 87 days. Increasing dietary concentrations of Aurantiochytrium sp. meal affected growth, feed efficiency, protein retention, and body DHA content positively. Fish fed Aurantiochytrium sp. meal had significantly greater weight gains when compared to fish fed the CLO diet. The dietary supplementation of Aurantiochytrium sp. meal also positively influenced the n-3 fatty acid profile in the muscle of the Nile tilapia, resulting in higher DHA concentrations. Fish fed the CLO diet accumulated significantly more DHA, compared to those fed the 1.0 g 100 g−1Aurantiochytrium sp. meal. The digestibility of selected nutrients from the Aurantiochytrium sp. meal was determined in fish weighing 16.01 ± 0.68 g, at 22 °C. DHA had high digestibility (96.05%) in Nile tilapia, even at the suboptimal temperature, but the digestibility of proteins, lipids, and saturated fatty acids, were decreased. In this study, we found supplementation of Aurantiochytrium sp. meal at 0.43 to 1.00 g 100−1 dry diet for Nile tilapia kept at 22 °C resulted in best growth, feed efficiency, body lipid composition, and adequate n-3/n-6 polyunsaturated-fatty-acid ratio in the muscle for human consumption.