This study evaluated the comparative effects of free silymarin (FS) and nanomicelle silymarin (NS) supplementation on growth, antioxidant defenses, and fatty acid composition in Caspian trout (Salmo caspius) larvae. Larvae (0.27 ± 0.01 g) were randomly assigned to triplicate groups and fed either control, FS (200 mg kg⁻¹), or NS (200 mg kg⁻¹) for 60 days. Growth performance indices, antioxidant enzyme activities, fatty acid composition, and leukocyte differentials were assessed. Results showed that NS supplementation significantly improved final weight, weight gain, and specific growth rate compared to both FS and control groups (p < 0.05), while FS had no significant effect on growth. NS-fed fish exhibited higher glutathione peroxidase (GPx) activity, elevated whole-body polyunsaturated fatty acids (PUFA), and increased deposition of long-chain n-3 fatty acids, particularly EPA and DHA. Superoxide dismutase (SOD) activity, malondialdehyde (MDA) levels, and leukocyte differentials did not differ significantly among treatments. These findings demonstrate that nanomicelle encapsulation can markedly improve the biological performance of silymarin in Caspian trout larvae, supporting improved growth and antioxidant resilience while enriching physiologically important fatty acids. Nanomicelle delivery systems may therefore represent a practical strategy to optimize phytochemical use in salmonid aquaculture, particularly during early life stages when fish are most vulnerable to stress.
