AT SUBOPTIMAL LOW TEMPERATURE, DIETARY SUPPLEMENTATION OF Aurantiochytrium sp. MEAL IN NILE TILAPIA DIETS PROMOTED HIGHEST GROWTH THAN COD LIVER OIL

Many of the nutritional requirements of  Nile  tilapia are known; however, further understanding  is necessary about  the dietary requirement of fatty  acid at suboptimal  low temperatures .  The beneficial effects of dietary poly unsaturated fatty acids  (PUFA)  to membrane function in ectothermic animals such as fish is well documented.  Therefore, we evaluated the dietary supplementation of two different sources of docosahexaenoic-acid (DHA, 22:6 n-3) to  Nile tilapia juveniles (8.47 ± 0.19 g) kept at a water temperature of 22° C. Such temperature simulates winter conditions in Southern Brazil, where the highest production of tilapia occurs in that country. Supplementation of Aurantiochytrium sp. meal  (AM) or cod liver oil  (CLO)  were evaluated  on  growth, cholesterol , glycogen  and lipid contents in the hepatopancreas, as well as  the fatty acid profiles of whole body, muscle, and hepatopancreas. AM is composed of a heterotrophic microorganism rich in DHA (16 g 100 g^-1 dry weight) and it is  produced by Alltech Inc. (Nicholasville, KY, USA). Three practical diets were tested, which contained:  1)  1.0 g AM 100 g^-1 dry diet, 2) 2.0 g CLO 100 g^-1,  and  3)  a control diet without n-3 fatty acids, with  swine  lard as the  sole lipid source. Both DHA-rich diets contained similar DHA contents (~0.20 g 100 g^-1). Fish were fed the experimental diets twice a day to apparent satiation during 87 days. The study followed a completely randomized design, with five replicates per dietary treatment and the level of significance adopted was 5% .  Fish fed the diet supplemented with AM presented 5.3% and 16.2% highest weight gain than  those fed the CLO and the control diets, respectively (Figure 1). However, f ish fed the CLO diet  showed  the highest DHA in the  whole body, muscle, and hepatopancreas but  presented  the lowest lipid and cholesterol contents in the hepatopancreas .  A digestibility trial was also performed at 22 °C  to evaluate the utilization of AM  nutrients by Nile tilapia weighing 16.01 ± 0.68 g. DHA presented high digestibility (96.05%) for Nile tilapia, even at a suboptimal temperature, but the digestibility of protein, lipid, and saturated fatty acids, decreased. The supplementation of  1.0 g AM 100 g^-1 dry diet improves productive performance and the supplementation of CLO improves the concentration of  n-3 PUFA in the body, muscle, and hepatopancreas  in Nile tilapia kept at 22 °C . Thus, either CLO or AM are potential additives in winter diets for Nile tilapia .  Additionally,  lipid sources with  different  dietary fatty acid profiles , such as the ones tested here, interfere on lipid metabolism and their inclusion should be made with caution,  especially at cold temperatures.