Modulatory Effects of Probiotics or Bio-Selenium Nanoparticles on Performance, Immunity, Redox Balance, and Microbial Load in Acrylamide-Challenged Oreochromis niloticus

The trial aims to investigate the possible protective role of a probiotic mixture or dietary administration of selenium nanoparticles against the toxic influences of waterborne acrylamide (ACR) in terms of growth, feed efficiency, blood biochemistry, antioxidant and immunological indices, fish flesh chemical composition, bacterial load, and tissue pathological architecture of Oreochromis niloticus. A total of 350 apparent healthy fish were allocated into equal seven treatments, each with five replicates. Each replicate contained 10 fish, resulting in 50 fish per group. The feeding trial was conducted over a period of 26 days using formulated diets and uncontaminated water. Following this feeding phase, the fish were exposed for an additional 30 days to acrylamide (ACR) at a concentration equivalent to 1/10 of the 96-hour LC₅₀ (34.6 mg/L), to evaluate the protective effects of the dietary treatments under sublethal toxic stress conditions. The first group was control and received a basal diet (CTR). While, the 2^nd (ACR+ PM1), 3^rd (ACR+PM2), 4^th (ACR+PM3), 5^th (ACR+SeNPs1), 6^th (ACR+SeNPs2), and 7^th (ACR+SeNPs3) groups were fed experimental diets containing varying amounts of probiotic mixture (1, 2, or 3 g PM per kg of diet) or SeNPs (1, 2, or 3 mg SeNPs per kg of diet), respectively. The results showed that the fish group fed diets supplemented with the highest level of SeNPs (3 mg SeNPs) had the best growth and feed efficiency indices. Following this, the fish group fed diets supplemented with a low level of both PM or SeNPs also showed positive results on total consumed feed, feed conversion ratio and specific growth rate. A significant reduce in liver function enzymes (ALT and AST) and kidney enzymes (uric acid and creatinine) was observed when fish diets were supplemented with a low level of SeNPs (1 mg SeNPs) after exposure to ACR. Conversely, there was a significant increase (P < 0.01) in serum levels of protein constituents (total protein and albumin) when fish feed was supplemented with a low level of probiotic mixture (PM1) in response to ACR exposure. Increasing the level of PM (2 or 3 g PM) in fish feed caused in a notable increase (P < 0.05) in complement activity (C3), innate immune response (lysozyme), redox status (SOD, GSH and TAC), acetylcholine esterase (AChE), and pro-inflammatory cytokines (IL-1b). It also caused a reduction in the levels of immunoglobulin antibodies (IgA and IgM) and malonaldehyde (MDA) levels in response to ACR toxicity. Furthermore, the chemical analysis of fish flesh indicated that there was no significant influence from dietary supplemented additives, despite the fact that all additives showed a high organic matter content (P <0.01) compared to the un-supplemented groups (CTR) under ACR toxicity. Feeding fish exposed to ACR with diets containing high amounts of SeNPs significantly elevated the lactic acid bacterial count and declined the total bacterial count in both the rearing water and intestinal samples. The fish exposed to ACR showed improved gill, liver, and spleen tissue architecture when given a dietary probiotic mixture (either PM1 or PM3) or SeNPs. It is worth noting that including 2 or 3 g of PM or 3 mg of SeNPs in the Nile Tilapia diet directed to the best health status and productivity during exposure to ACR.