Selenium is an essential mineral for animals and crucial for animal metabolism, impacting growth, reproduction, antioxidant capacity, immunity, and muscle nutrition. Therefore, adequate dietary selenium is vital in animal production. Organic selenium, particularly selenium yeast offers higher utilization, stable structure, and lower toxicity than inorganic selenium. The largemouth bass (Micropterus salmoide), a carnivorous fish native to California, is extensively farmed in China for its rapid growth, appealing appearance, adaptability, short breeding cycle, spineless meat, and high nutritional value. This study aims to investigate the effects of selenium yeast on the hemocytes antioxidant capacity and apoptosis, as well as the morphological histology in largemouth bass.
The feeding experiments were conducted in an indoor recirculating water system (natural light cycle). The five iso-nitrogen and iso- lipid feeds were supplemented with selenium yeast levels of 0, 0.5, 1.0, 1.5 and 2.0 mg/kg, respectively. Largemouth bass (initial body weight: 11.48 ± 0.43 g) were randomly and equally distributed among 15 tanks, with 35 fish in each tank. The feeding experiment was conducted for 67 days with daily apparent satiation feedings at 9:00 and 16:00. During the feeding period, dissolved oxygen concentration was between 6.00-7.88 mg/L, pH level was 7.7-7.9, water temperature range was 25.5-31.5 °C, nitrite content was lower than 0.002 mg/L, and ammonia nitrogen content was not higher than 0.1 mg/L.
After 67 days, based on the growth, liver histology, and serum antioxidant performance of largemouth bass, the addition of selenium yeast should not exceed 1.5 mg/kg. However, supplementation with 1.5 mg/kg of selenium yeast can improve the antioxidant capacity of hematocyte and inhibit the apoptosis. However, the addition of selenium yeast should not exceed 1.5 mg/kg.