Bioactive substances such as β-carotene are regarded as an effective dietary aquafeed supplement to boost the
immunity of fish cultured in high densities. The present study aimed to evaluate the influence of the dietary
incorporation of β-carotene derived from Spirulina platensis (0, 0.5, and 1.0 g kg− 1 diets) on growth performance,
feed efficiency, hemato-biochemical indices, immunological responses, hepatic antioxidant enzymes, and associated immune-antioxidant genes expression in Nile tilapia, Oreochromis niloticus fingerlings (initial weight of
5.85 ± 0.06 g) reared at two stocking densities (SD100, 100 fish m− 3 and SD200, 200 fish m− 3) for 70 days. Fish
were randomly allocated into eighteen plastic tanks (0.5 m3 each plastic tank) in triplicate and fed three times
per day at 9:00 a.m., 11:00 a.m., and 3:00 p.m. with three isonitrogenous and isolipidic diets. The results showed
that there was no difference in feed intake among the experimental diets (P > 0.05). The diet containing
0.5 g kg− 1 β-carotene increased weight gain, final body weight, specific growth rate, and feed conversion ratio of
fish reared at SD200. Fish grown at SD100 or SD200 showed a significant increase in hematocrit and hemoglobin
levels when fed a diet supplemented with 0.5 or 1.0 g kg− 1 β-carotene compared to those on an unsupplemented
diet (P < 0.05). Alanine amino transferase and aspartate amino transferase levels were lowest in fish group fed
diet containing 1.0 g kg− 1 β-carotene at SD100 as well as in fish fed diet supplemented with 0.5 and 1.0 g kg− 1
β-carotene at SD200. Fish raised at SD200 and supplemented with 1.0 g kg− 1β-carotene showed significantly
improvements in total protein, albumin, and growth hormone levels compared to those fed on an unsupplemented diets (P > 0.05). Supplementing with 0.5 or 1.0 g kg− 1 β-carotene diets significantly increased
the concentrations of C3, C4, and IgM in fish reared at both SD100 and SD200 compared to those without supplementation (P < 0.05). The hepatic antioxidant activity of malondialdehyde was lowest in fish-fed diet supplemented with 1.0 g kg− 1 β-carotene at SD100. At SD200, fish fed a diet supplemented with 1.0 g kg− 1 β-carotene
showed the highest levels of glutathione (GSH) and glutathione peroxidase (GPx) activity (P < 0.05). The highest
activity of catalase (CAT) was in fish fed diet supplemented with 0.5 g kg− 1 β-carotene at SD200 and SD100
whereas, the highest activity of superoxide dismutase (SOD) was in fish fed diet supplemented with 1.0 g kg− 1
β-carotene at SD100. The same trend was seen in the associated hepatic genes expression of superoxide dismutase
2, CAT, and GPx. When compared to other diets, fish raised at SD100 and fed a diet supplemented with 0.5 g kg− 1
β-carotene showed the highest levels of gene expression for interleukin (IL)− 1β and interleukin-8 (IL-8) (P <
0.05). But those reared at SD200 and fed a diet without β-carotene supplementation had the lowest transcript
expressions of IL-1β and IL-8. In conclusion, adding β-carotene up to 1.0 g kg− 1 to the basal diet improves and
boosts growth performance, feed efficiency, immunological responses, hepatic antioxidant enzyme, and associated immune-antioxidant gene expression in Nile tilapia reared at SD200 |
