In shrimp aquaculture, the use of fishmeal and fish oil is still common, but the inclusion levels have dropped over the last years, due to environmental, economic and availability challenges. At the same time shrimp production has been increasing, so alternative ingredients like plant materials are used progressively. This causes several challenges since the fats and proteins used as alternatives for fishmeal and fish oil are sub-optimal, with a consequent decrease in growth performance. Additionally, the selenium content in the feeds and shrimp body is decreasing, which causes a decreased growth performance and health status of shrimps. To counteract this, fish farmers and feed formulators can add selenium and/or nutritional emulsifiers to the diet. The goal of this experiment was to evaluate the efficacy of different selenium sources and the use of a nutritional emulsifier based on castor oil on growth performance and feed efficiency.
Shrimp were fed four different diets; 1. Control diet, low in fishmeal (10%) and fish oil (1%) without any added selenium; 2. Diet SS, control diet + 0.5 ppm selenium from sodium selenite, 3. Diet SM, control diet + 0.5 ppm selenium from L-selenomethionine; 4. Diet SMNE, Control diet + 0.5 ppm selenium from L-selenomethionine + 500 ppm nutritional emulsifier based on castor oil. During the 8-week feeding trial, the fish were analyzed for growth performance and feed efficiency every fortnight. The parameters analyzed were: total biomass, individual weight, weight gain (WG), average daily gain (ADG), specific growth rate (SGR), feed intake (FI), feed conversion ratio (FCR) and survival rate (S).
Overall, the inclusion of inorganic selenium, as sodium selenite, did not affect growth performance, only the specific growth rate was significantly improved by using diet SS in comparison with control diet.. In sharp contrast, when shrimp were fed diet SM and diet SMNE, tank biomass, individual weight, weight gain, average daily gain and specific growth rate were all significantly improved compared to both the control diet and diet SS. On top off this, shrimp immunity and antioxidant status were significantly improved in all shrimp fed selenium-rich diets, again showing the significantly best results in diets SM and SMNE.
In conclusion, the addition of selenium can be beneficial for shrimp growth performance, feed efficiency and health. However, it is important to pick the right, organic source. In this experiment. L-selenomethionine is shown to be more efficient compared to sodium selenite. Additionally, it can be observed that adding a nutritional emulsifier can further improve shrimp growth performance and health.