This study investigated the effects of dietary chitosan-stabilized selenium nanoparticles (SeNPs) on growth, physiological status, immunity, antioxidant activity, digestive enzymes, and muscle histology in Litopenaeus vannamei. A total of 240 healthy shrimps (2.94 ± 0.03 g) were randomly assigned to four dietary groups (control, SeNP1: 0.4 mg/kg, SeNP2: 0.8 mg/kg, SeNP3: 1.2 mg/kg), with four replicates per group and 20 shrimp per replicate. Over a 14-week feeding trial, shrimp fed SeNP-supplemented diets exhibited significantly enhanced growth performance, particularly in the SeNP2 group, as reflected in final body weight, total body weight gain, specific growth rate, and protein efficiency ratio (P ≤ 0.0001). Additionally, feed conversion ratio was significantly improved in SeNP2 (P ≤ 0.0001), indicating superior feed utilization. Meanwhile, hepatic biomarkers (Alanine aminotransferase, ALT; Aspartate aminotransferase, AST) were significantly decreased (P ≤ 0.0001) with increasing SeNPs level within shrimp feed, suggesting improved liver function. Whereas, renal parameters such as uric acid were reduced in SeNP3 (P ≤ 0.01) and creatinine showed a significant linear trend (P ≤ 0.01). Moreover, cortisol levels were significantly lower in SeNP2 (P ≤ 0.05), and glucose (P ≤ 0.01) and triglyceride levels (P ≤ 0.0001) were modulated, reflecting improved metabolic resilience. Also, SeNP2 elevated shrimp haemolymph antioxidant markers, including catalase (P ≤ 0.01), total antioxidant capacity (P ≤ 0.01), and superoxide dismutase (linear trend: P ≤ 0.05), while malondialdehyde declined (P ≤ 0.05). Meanwhile, lysozyme activity was significantly enhanced (P ≤ 0.05), indicating haemolymph innate immune remarks stimulation. Furthermore, anterior intestine digestive enzyme activities, especially amylase (linear trend: P ≤ 0.05) and lipase (P ≤ 0.05), increased with the highest SeNP supplementation level. Herein, histological observations confirmed progressive improvement in muscle structure, and muscle fibre thickness was significantly highest in SeNP3 (P ≤ 0.001), though SeNP2 achieved the best overall physiological outcomes. In conclusion, dietary supplementation with 0.8 mg/kg SeNPs (SeNP2) is recommended as the optimal level for enhancing shrimp growth, health status, and tissue integrity under aquaculture conditions.