Nile tilapia
Dietary n-3 fatty acid for Nile tilapia at optimal and suboptimal-cold temperature by Renata Oselame Nobrega and Débora Machado Fracalossi, Fish Nutrition Lab (LABNUTRI), Aquaculture Department, Federal University of Santa Catarina (UFSC), Florianópolis, Brazil
T
he studies conducted in recent years by our group at LabNutri showed that growth and feed efficiency of Nile tilapia at a suboptimal cold temperature (22 °C) were improved when fish were fed diets containing polyunsaturated n-3 fatty acids (n-3 PUFA). Despite being a tropical species, Nile tilapia is farmed in many subtropical regions worldwide. In Brazil, Paraná state, the largest producer of Nile tilapia is located in a subtropical climate region. However, cold-suboptimal temperatures have been reported worldwide as causing negative impacts on Nile tilapia production. Our studies show that when juvenile Nile tilapia of the GIFT strain, sexually inverted to male, are subjected to cold-suboptimal water temperatures (22°C), there is a reduction of 40-to-50 percent in feed consumption, which leads to a significant decrease in growth when compared to fish kept at an optimal growth temperature (28 °C). The ideal water temperature range for Nile tilapia farming is from 26-to-30 °C. However, the temperature range at which feeding and voluntary movement cease as well as the lethal temperature are influenced mostly by genetics and nutrition. For instance, the fatty acid profile of the diets, specifically the ratio between polyunsaturated fatty acids (PUFA) and saturated fatty acids (SFA), can affect growth at lower temperatures. Thus, we can formulate winter diets for Nile tilapia to promote growth. Of course, farming Nile tilapia strains, which are more tolerant to suboptimal water temperatures, could also be beneficial. However, such strains are not easily obtained. Changes in ambient temperature affect the requirements of fatty acids in the diets of ectothermic animals such as fish, which do not maintain a constant body temperature. Thus, to maintain their physiological function in cold unfavorable temperatures, fish increase the fatty acid unsaturation levels of the phospholipids that make up their cell membranes. The higher the degree of unsaturation of a particular fatty acid, the lower its fusion point. This is an adaptive mechanism which enables cell membranes to function properly when temperature variations occur. Despite having numerous studies on Nile tilapia nutrition, there are still areas that need further understanding such as the dietary
requirement and metabolism of fatty acids at different farming temperatures. Traditionally, Nile tilapia reared at optimal temperature have been considered to have a dietary requirement of only 18-carbon chain fatty acids, such as alpha-linolenic acid (18: 3 n-3, α-LNA) and/or linoleic acid (18: 2 n-6, LOA) (Takeuchi et al., 1983; Chen et al., 2013). Our results demonstrate that a dietary n-3/n-6 ratio varying from 0.2-to-2.9 does not affect the growth of Nile tilapia juveniles when kept at optimal temperature. In that study, a total dietary PUFA of 1.30 percent diet dry weight was enough to promote a high weight gain (Mufatto et al., 2019). However, at suboptimal cold temperature, Nile tilapia growth and feed efficiency were improved when fed diets containing fish oil, rich in n-3 long-chain polyunsaturated fatty acids (n-3 LCPUFA), if compared to fish fed diets with other sources of lipids,
rich in LOA or α-LNA (Corrêa et al., 2017; Corrêa et al., 2018). Likewise, the dietary requirement of α-LNA of Nile tilapia was higher when fish were reared at suboptimal-cold temperatures when compared to fish reared at optimal temperatures (Nobrega et al., 2017). Nowadays there is a search for sustainable alternatives to fish meal and fish oil as feed ingredients. Although plant oils have been used to substitute fish oil, there is a wide difference in their fatty acid profile, mainly in their content of n-3 PUFA.
24 | October 2019 - International Aquafeed