1600 Largemouth bass with initial body weight of 19.27g were fed two diets of control diet or Selenomethionie addition diet for 8 weeks in pond cages for growth performance test. The Selenomethionie addition dosage is 0.48mg/Kg. The Se content in control diet was 1.387mg/Kg, and 1.780mg/mg in Selenomethionine addition diet. After growth trial, 420 Largemouth bass from each treatment were randomly selected for stress tests in tanks. Each stess standed for 30h and 60 fish for each stress. 7 stress conditions include 32℃ high temperature stress, 8℃ low temperature stress, 4mg/L ammonia nitrogen stress, 2mg/L nitrite stress, transport stress, 1% salinity stress and 1-2mg/L low oxygen stress. After 30h of stress, fishes were return to pond cages for 14d and go on fed with control diet or Selenomethionie addition diet according to their initial treatment.
After 8 weeks of growth, Selenomethionie addition significantly improved Largemouth bass growth performance. The body weight gain rate was improved for 4.68% (P≤0.05)，FCR was decreased 4.30% (P≤0.05). Selenothionine addition had significantly improved Se content in fish flesh.
Selenomethionine addition had improved fish survival in 30h of stresses. There had 22 fishes died of 60 largemouth bass fed control diet after 30h of high temperature stress. 8 fishes died of 60 largemouth bass fed control diet after 30h of ammonia nitrogen stress. And 2 fishes died of 60 largemouth bass fed control diet after 30h of cold temperature stress. There was no fish died in Selenomethionine addition diet in any stress conditions.
In followed 14d of feeding trial after 30h of stress, the death of fish of both treatments were seriously. However, Selenomethionine treated fish have higher survival. For total 420 fish, the control diet have 38 survival, and Selenomethionine treated fish have 69 survival.
In conclusion, addition Selenomethionine in Largemouth bass diet improved fish growth performance and improved fish stress resistance in hot temperature, ammonia nitrogen and low oxygen conditions and improved fish bacteria resistance after stress with higher survival after stress and go on infection conditions.