Effects of geraniol on oxidative stress, apoptosis, and immunoinflammatory responses in hybrid grouper (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂) during live transport.

This study evaluated the protective effects of geraniol (Ger) in hybrid grouper (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂) during 72 h of simulated live transport. Fish were assigned to four groups: control (CK) and Ger-treated groups at 20 mg/L (Ger20), 30 mg/L (Ger30), and 40 mg/L (Ger40). With prolonged transport, Kaplan-Meier estimated survival in the CK group declined to 50.60% at 72 h. The Ger-treated groups showed higher estimated survival at 72 h than CK, and Ger30 maintained 100.00% throughout the transport period. Transport stress induced marked oxidative responses in the CK, as reflected by elevated antioxidant enzyme activities and malondialdehyde (MDA) accumulation. Ger treatment, particularly Ger30, was associated with lower MDA accumulation and more moderate changes in antioxidant enzyme activities. Ger also affected transport-associated tissue injury indicators, with Ger30 generally showing lower AST activity and better preservation of gill morphology, whereas Ger40 showed marked ALT elevation at 48 h. In addition, Ger30 was associated with more moderate fluctuations in lysozyme (LZM) activity and relatively high immunoglobulin M (IgM) levels during the middle and late stages of transport. Stress-related gene-expression patterns in Ger30 suggested a more balanced response to transport stress. Overall, Ger exhibited a non-monotonic dose-response pattern, with 30 mg/L representing the most favorable intermediate concentration, whereas 40 mg/L provided no additional improvement and produced less favorable responses in several indicators.