ISSUE FOCUS FEED & ADDITIVE MAGAZINE August 2025 33 2022). Alltech’s selenium-enriched Saccharomyces cerevisiae yeast (Sel-Plex®) was the first selenized yeast to receive EU authorization as a nutritional additive for all species and was the first FDA-reviewed organic selenium source. Its superior bioavailability, compared to inorganic sources, is attributed to selenomethionine. Several studies have already investigated the potential effects of specific organic-selenium-enriched dietary strategies on oxidative stress and thermal stress responses in aquatic species (Figure 2). For example, research by Elfadadny et al. (2024) investigated antioxidant enzyme expression (GPx, GST and SOD) in all tissues of P. vannamei after heat stress (33°C). The same study reported variations in GSH levels and MDA content between treatment groups. Similarly, Ilham and Fotedar (2016), examining the effects of dietary strategy changes on yellowtail kingfish (Seriola lalandi) under elevated temperatures (26°C), observed variations in red blood cell glutathione peroxidase (GPx) activity and muscle selenium levels. In addition, recent research on rainbow trout suggested that fish acclimated to higher temperatures and receiving organic selenium-specific dietary interventions displayed differences in stress-related responses, including changes in expression levels of heat-shock proteins and cortisol levels (Hosseinpour et al., 2024). Apart from oxidative stress, temperature fluctuations can disrupt the intestinal microbiome’s equilibrium, promote the overgrowth of pathogenic bacteria, and weaken the intestinal barrier (Zhao et al., 2024). Therefore, maintaining gut health is Gill GSH (µmol/L) MDA concentration (µmol/L) Mean RBC GPxactivity (U/g Hb) Muscle Se (mg/kg diet) bc 20 15 10 5 0 120 110 100 90 80 70 60 50 4 3 2 1 0 30 25 20 15 10 5 0 a cd a c a a b b a b b Muscle Control Control 2 mg Organic Se 2 mg Organic Se 4 mg Organic Se 4 mg Organic Se Control Organic Se Control a b a a c bc Organic Se Hepatopancreas Penaeus Vannamei Shrimp Yellowtail Kingfish Gill Muscle Hepatopancreas Figure 2. Reduced glutathione (GSH) and malondialdehyde (MDA) content in the gill, muscle and hepatopancreas of Penaeus vannamei shrimp fed control and organic selenium (Se) diets under induced heat stress challenge for 6 h at 33°C (Elfadadny et al., 2024), and red blood cell glutathione peroxidase (GPx) activity and muscle selenium concentration in yellowtail kingfish fed control and organic selenium (Se) diets under elevated temperatures at 26°C (Ilham and Fotedar, 2016)
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