Shrimp aquaculture has experienced decades of exponential growth, and the expectation is that this growth will continue in the coming years. However, because of the increased intensity and volume of production, challenges arise for the sector to maintain this steady growth. For example, the increased disease pressure is endangering shrimp farming practices. Whilst in the past a lot of antibiotics were used to tackle diseases , the increasing concerns of antimicrobial resistance created a need to develop alternatives. One viable way to improve disease resilience of shrimp is by supplementing the diet with additives that can improve the overall health status of animals. Selenium is an important component of the diet and can play a vital role in the antioxidant and immune system. However, knowledge about the inclusion levels and the effect of different sources is still limited in shrimp aquaculture . The goal of this experiment was to evaluate the efficacy of different selenium sources on growth performance , feed efficiency and disease resistance against a Vibrio parahaemolyticus challenge .
Shrimp were fed three different diets; 1. Control diet, 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 (Excential Selenium 4000, Orffa Additives BV) . During the 8-week feeding trial, the fish were analyzed for growth performance and feed efficiency every fortnight . Additionally, immune and antioxidant parameters were measured after 8 weeks of feeding, and at the same time, the Vibrio count in the hepatopancreas and intestine was measured. After the feeding trial, the shrimp were challenged with Vibrio parahaemolyticus . Over the next 15 days, the shrimp were monitored and mortalities were determined. At the end of this challenge period (d15), immune- and antioxidant parameters, as well as Vibrio count, were determined. All parameters were statistically compared by one way ANOVAs.
Growth performance was significantly improved (P<0.05) by inclusion of L-selenomethionine but not sodium selenite . Both sources of selenium significantly improved the FCR of white leg shrimp (P<0.05) with organic selenium, in the form of L-selenomethionine, leading to significantly lower FCR compared to sodium selenite (Figure 1) .
Selenium, regardless of the source, improved the immune and antioxidant capacity of white leg shrimp. L-selenomethionine in the diet was shown to significantly reduce the Vibrio count in the shrimp (P<0.05) , whilst sodium selenite did not. Survival rate after the challenge was significantly higher for shrimp receiving the L-selenomethionine addition (P=0.027) compared to control and sodium selenite addition (Figure 2).
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 significantly more efficient compared to sodium selenite.