To evaluate the effects of different organic selenium sources on rice field eel (Monopterus albus), four isonitrogenous and isolipidic diets were tested: a control (no supplement) and four diets each supplemented with 0.24 mg/kg selenium as diselenoacetic acid (Se1), diselenopropionic acid (Se2), diselenobutyric acid (Se3), or diselenodibutyric acid (Se4). Rice field eels (initial body weight 18.43 ± 0.03 g) were fed for 60 days. The Se1 group showed significantly higher WGR and SGR than the control. Whole-body crude protein was significantly increased in the Se3 and Se4 groups, while crude lipid content was significantly decreased in Se1, Se3, and Se4 groups. Selenium concentrations in the liver and kidney were highest in the Se2 group. Serum AST and ALT activities were decreased in Se4. In the Se4 group, intestinal CAT, T-SOD, and GSH-PX activities were enhanced, along with upregulation of Gpx8, CAT, Nrf2, and Keap1. Hepatic CAT and GSH-PX increased in Se2 and Se4, with Gpx8 upregulated in Se1. Intestinal lipase activity was significantly increased in Se2. At the phylum level, Proteobacteria predominated. At the genus level, Cetobacterium predominated. In summary, diselenoacetic acid enhanced growth, while diselenopropionic acid and diselenodibutyric acid improved antioxidant defense and intestinal health in rice field eel.

In this study, C. pyrenoidosa were cultured with seven different concentrations of Na₂SeO₄ (0–10 mg/L), and the effects of Na₂SeO₄ on the growth, Se-forms, and nutritional quality of C. pyrenoidosa were explored. The results showed that at the concentration of 0.5 mg/L Na₂SeO₄, the C. pyrenoidosa were plump and healthy; the contents of biomass, soluble protein, lipids, and TPUFA reached the highest level; the total Se content in C. pyrenoidosa increased with the increasing Na₂SeO₄ concentrations. However, the proportion of organic Se in C. pyrenoidosa. reached the highest value of 87.58% at the concentration of 0.5 mg/L Na₂SeO₄. Among organic Se forms, SeMet accounted for the largest proportion, while MeSeCys accounted for a relatively smaller proportion, but SeCys₂ was not detected. The addition of Na₂SeO₄ (except for ≤0.5 mg/L) reduced the contents of photosynthetic pigments in C. pyrenoidosa. In addition, the antioxidant capacity of C. pyrenoidosa first increased and then decreased with the increasing Na₂SeO₄ concentrations, but different enzymes exhibited different tolerances to Na₂SeO₄. Based on the above research results, 0.5 mg/L Na₂SeO₄ concentration is recommended for the production of Se-rich C. pyrenoidosa. Our findings will provide a theoretical basis and practical references for the development of Se-rich C. pyrenoidosa health care products.