Effect of Organic and Nano Selenium Dietary Supplementation on Growth, Survival, Feed Utilization, Gastrointestinal Health, and GPx Enzyme Activity of Gilthead Sea Bream (Sparus aurata) Larvae

In this study, gilthead sea bream (G. Sea bream) larvae were fed three different micro diets (MD) during the weaning period, each containing 51.7% crude protein. The diets included: an MD supplemented with 4 mg of organic selenium per kilogram (Org-Se), an MD supplemented with 0.3 mg of nano-selenium per kilogram (Nano-Se), and a control MD without Selenium supplementation (C). The hatched larvae were fed live food (microgreen algae, rotifers, and Artemia) in addition to the MD. Using nine 5 m³ fiberglass tanks under a greenhouse, the experiment began with G. Sea bream larvae at 20 days post-hatch (DPH) and continued until the end of the trial at 60 DPH. The brood fish from which the larvae were derived received the same Selenium forms and doses in their basal diets, which consisted of a mix of 45% protein dry feed, squid, and sardines. Data on the broodstock and their offspring were reported in a separate research paper. The larvae, initially weighing 2.4 mg and measuring 4.5 mm in length, were replicated three times across the three treatments, with 50,000 larvae per tank (4 m ³ of seawater). The larvae fed the Nano-Se diet exhibited a higher survival rate of 57.43%, compared to 54.76% for those on the Org-Se diet and 53.73% for the control diet (P < 0.01). The Nano-Se diet also produced the highest growth indices (FBW, SGR, FTL, and condition factor, K) and surpassed both the control and Org-Se diets. However, differences among the three treatments were not significant for FCR and PER (P > 0.05). The study showed that the GPx enzyme activity in 20 DPH larvae from broodstock fed the Nano-Se diet was 10.34 U/mg of protein, significantly higher than that of larvae fed the Org-Se diet (9.36 U/mg of protein) and the control diet (8.81 U/mg of protein) (P ≤ 0.05). Additionally, after 60 DPH, the larvae on the Nano-Se diet exhibited the highest GPx enzyme activity at 17.6 U/mg of protein, followed by the Org-Se at 15.54 U/mg of protein and the control diet at 13.33 U/mg of protein (P < 0.01).