Abstract
Background:
Organic selenium (Sel-Plex®) supplementation holds a considerable promise for improving the effectiveness of fish production.
Aim:
This experiment was accomplished to judge the potential benefits of Sel-Plex® nutritional additive on growth outcomes, physiological response, oxidative status, and immunity-linked gene expression in Nile tilapia (Oreochromis niloticus) fingerlings exposed to bacterial infection with Aeromonas hydrophila.
Methods:
Utilizing a basal diet of 30% protein, four experimental diets were prepared, each of which contained Sel-Plex® at concentrations of 0.0, 0.5, 1, and 2 mg/kg, respectively. Three replicates of 20 fish/treatment were used using 240 healthy Nile tilapia fingerlings. Fish were placed in twelve glass aquariums and separated into four groups at random. For the entire span of 8 weeks, diets were admitted to fish at a 3% rate of fish biomass/aquarium. After the feeding trial, pathogenic Aeromonas hydrophila was intraperitoneally injected into fish of each treatment, and fish were observed for fifteen days to track the survival rate after the challenge.
Results:
Growth performance, physiological response, immunological parameters (Phagocytic activity, Phagocytic index, and Lysozyme), and antioxidant parameters (Catalase, Superoxide dismutase, Malondialdehyde, and Glutathione Peroxidase) were noticeably improved in Sel-Plex® treated groups. Moreover, Sel-Plex® increased gene expression linked with the immune system in the liver (TNF-α, and IL-1β), to growth (IGF-1, and GHr), and antioxidants (SOD, and GSH-Px). Under pathogen-challenge conditions, the employed dietary Sel-Plex® supplementation could successfully lower fish oxidative stress, offering a potential preventive additive for Nile tilapia instead of antibiotics. On the other hand, Sel-Plex® significantly enhanced each of three intestinal morphological measurements (villus width, villus length, and crypt depth), demonstrating the greatest influence on the improvement of intestinal structure overall. In the Nile tilapia control group, the infection with A. hydrophila caused noticeable degenerative alterations in the gut, hepatopancreas, spleen, and posterior kidney. The severity of the lesion was significantly reduced and significantly improved with higher Sel-Plex® concentrations. Sel-Plex® supplemented groups had 100% survival rates among the A. hydrophila-challenged groups.
Conclusion:
It could be advised to enrich the diets of Nile tilapia fingerlings with 1-2 mg.kg−1 of Sel-Plex® to enhance growth rate, physiological response, immunological reaction, and intestinal absorptive capacity.

Key words: Aeromonas hydrophila, Immune-related gene expression, Nile tilapia, Organic selenium, Oxidative status