Nutritional benefits of microalga oil replacement in tilapia farming

Schizochytrium oil is currently the only commercially available microalgae oil to replace plant and fish oils in Nile tilapia diets, however there are some uncertainties on its benefits and optimal replacement level. To systematically evaluate the benefits of Schizochytrium in fish nutrition, a metanalysis was conducted. Its results indicated that an inclusion of Schizochytrium did not result in loss of omega-3 content of the fish fillet (SMD = 0.62; 95%CI = -0.51-1.76). To assess the effects on survival and changes in the gut microbiota (16S rRNA sequencing) of Nile tilapia, Schizochytrium oil was incorporated in the fish diet. Microalgae-oil in the diet increased growth rate without impacting on fish survival. Plant oil caused an increase in the abundance of Aeromonadaceae in the gut, but this was not the case with microalgae oil was used. To characterize the long-term effects of microalgae oil, Nile tilapia from the previous experiment were fed on the same diets for 11 months. Schizochytrium oil in the diet increased the omega-3 content of the Nile tilapia fillet up to 32.30±1.13%. The benefits of Schizochytrium oil replacement was also tested on Manyara tilapia (Oreochromis amphimelas), an endangered species. Schizochytrium oil increased fish growth and omega-3 content of the flesh up to 32.68±0.25%. Gonad development was not affected by Schizochytrium oil in the diet. The results of this thesis indicate, that Schizochytrium oil can replace fish-based oils in the diet of Nile tilapia without compromising survival or disrupting the composition of the gut-microbiome as plant-based diets do, whileat the same time improving growth and omega-3 content of the fillet in both Nile and Manyara tilapia thus representing a better alternative to fish oils than plant-based oils