Comparative study of dietary selenium sources on gilthead seabream ( Sparus aurata): Growth, nutrient utilization, stress response and final product quality

Selenium (Se) is a crucial trace mineral in human nutrition, known for its various health benefits, including the enhancement of antioxidant defenses. Enrichment of fish fillets with Se is seen as an interesting strategy to reduce the risk of Se deficiency in human diets. While inorganic sources have been traditionally used to supplement Se in fish diets, organic Se forms have demonstrated superior bioavailability and efficacy in managing oxidative stress and tissue retention rates compared to their inorganic counterparts. The main objective of this study was to assess the performance, stress resistance, and product quality of gilthead seabream (Sparus aurata) in response to diets supplemented with 0.2 mg kg(-1) of Na2SeO3 (CTRL), Zn-L-SeMet (AVSe) or OH-Se-Met (ORGSe), complying therefore with the European Food Safety Agency (EFSA) maximum allowed supplementation of organic Se (0.2 mg kg(-1)). Diets were formulated to be similar in their protein (48% DM) and lipid content (17% DM), and hand-fed to apparent satiety to quadruplicate groups of 20 fish (initial body weight similar to 75 g) gilthead seabream juveniles for 137 days. Fish were kept in a recirculating saltwater system (salinity 35 parts per thousand, 22 +/- 1 degrees C) until they reached commercial size (>250 g). At the end of the growth trial, all fish were individually weighed and measured, with 4 fish per tank sampled for whole-body composition analysis. Fillet yield, muscle lipid and mineral composition, and hepatic oxidative stress indicators were assessed (n = 12). Lipid peroxidation, muscle pH, water-holding capacity (WHC), color, and texture were evaluated on days 7 and 14 (n = 8), while sensory analysis was conducted on 20 fish. Additionally, 12 fish per treatment were subjected to overcrowding (100 kg m(-3)) for 5 min and air exposure for 1 min. After a 1-h recovery period, plasma and liver samples were collected from these fish, and results were compared to those of the non-stress group. All diets yielded equivalent growth performance, ensuring low feed conversion ratio. Fish fed the AVSe diet exhibited higher whole-body protein content compared to those fed the CTRL diet. Regarding mineral utilization, increased Se retention and gain in fish fed AVSe and ORGSe diets led to higher Se content in these fish compared to the CTRL. Additionally, the AVSe diet has also resulted in significantly increased Se deposition in the muscle compared to the other tested Se sources, contributing with 34% of the Se Daily Recommended Intake (DRI). The assessed flesh quality parameters and overall consumer acceptance did not reveal significant differences among the groups. Exposure to an acute stress was found to decrease the activities of Glutathione reductase and glutathione peroxidase, which in turn has increased the level of oxidized glutathione, particularly in the AVSe group. Compared to OH-Se-Met and Na2SeO3, Zn-L-SeMet was more effective in promoting response to stress and nutritional value of gilthead seabream as an important source of protein and Se in human diet.