Currently, deacetylated chitin (chitosan) nanoparticles (CNPs) are successfully utilized in aquaculture practices. This trial demonstrates the efficacy of CNPs in combating diazinon (DZN) toxicity in African catfish, Clarias gariepinus, via monitoring hepato-renal function, serum immune trait, hormonal function, and hepato-renal antioxidant activity. Four groups were allocated as follows: a control group, a CNPs group (0.66 ml/L CNPs), a DZN exposed group (0.598 ppm, 1/10 LC50), and a DZN + CNPs group (0.598 ppm DZN + 0.66 ml/L CNPs), all for 30 days. Exposure to 0.598 PPm DZN resulted in a severe decline in the immune parameters (albumin, globulin, immunoglobulins (IgG, IgM), and total proteins), neurological indicator, acetylcholinesterase (AchE), reproductive hormones (Testosterone (T.) and Luteinizing Hormone (LH)), and the superoxide dismutase (SOD) and total antioxidant capacity (TAC) readings in both hepatic and renal samples. Moreover, a clear increment in hepatic and renal indicators (AST, ALT, urea, and creatinine), lipid peroxidation (LPO), and some reproductive indices including follicle stimulating hormone (FSH) and serum 17-β estradiol (E2) was clearly increased. Interestingly, the dietary inclusion of CNPs markedly palliated the toxicity by DZN with significant improvement in the immune-reproductive indices, plus normalizing the values of hepato-renal function and augmenting the activity of antioxidant parameters. Thus, the present study demonstrates the efficacy of CNPs in mitigating low-dose DZN toxicity, resulting in significant improvements in physiological, biochemical, and reproductive parameters. This highlights the promising potential of CNPs as a viable strategy for enhancing the health of C. gariepinus, thereby promoting the sustainability of the aquaculture industry and safeguarding human health.