Cold snaps during the winter present a critical challenge for Asian seabass (Lates calcarifer) in Taiwan, as sudden temperature drops significantly affect their growth and survival. This study explores the effects of dietary grape extract (GE) from Vitis vinifera on the growth performance, oxidative stress regulation, and thermal tolerance of this commercially valuable fish. Over a 60-day feeding trial, four dietary groups were tested: a control diet without GE and three diets supplemented with GE at 2% (GE20), 3% (GE30), and 4% (GE40) with commercial feed. The results demonstrated that GE supplementation positively influenced growth, with the GE20 group achieving the best weight gain and feed conversion ratio among all groups. The upregulation of the growth-related gene igf-1 in the liver of the GE20 group further supported its superior growth performance. Additionally, GE-fed groups showed increased expression of antioxidant-related genes sod1 and sod2 in the liver, while gpx1 exhibited a significant increase only in the GE20 group, indicating enhanced antioxidant defenses. Cat gene expression remained unchanged, and higher GE doses reduced the expression of gpx1, cat, and igf-1. Furthermore, GE supplementation improved cold tolerance in all treated groups compared to the control. These findings suggest that dietary GE at 20 g/kg is particularly effective in enhancing growth performance and cold tolerance in Asian seabass, offering a promising strategy for boosting fish health and adaptability in aquaculture.

Temperature fluctuations pose significant physiological challenges for aquatic ectotherms, and cold stress is known to disrupt cellular energetics and mitochondrial function. Mitochondria play central roles in cold adaptation, yet how environmental salinity modulates these responses remains poorly understood. In this study, we investigated the effects of freshwater (FW) and seawater (SW) acclimation on hepatic mitochondrial dynamics, biogenesis, and bioenergetic regulation during hypothermal stress in Indian medaka. Fish acclimated to FW or SW were exposed to 18 °C or 15 °C for up to 168 h. At 18 °C, PGC-1α expression increased in both salinity groups, whereas TFAM was significantly upregulated only in FW fish. mtDNA copy number remained unchanged at 18 °C but increased transiently at 15 °C in both groups, returning to baseline more rapidly in SW fish. CS abundance increased early in both groups and remained elevated longer in SW fish. COX1 showed a transient elevation at 18 °C but declined in FW fish at 15 °C, whereas COX4 was induced only in SW fish at 15 °C. Cytoplasmic and mitochondrial DRP1 responses were faster and more transient in SW fish, whereas VDAC1 abundance remained stable in SW fish but fluctuated in FW fish. Liver transcriptomic profiling at 18 °C identified 142 FW-specific DEGs, 109 SW-specific DEGs, and 240 shared DEGs. FW-enriched pathways were mainly associated with stress response and biosynthetic processes, whereas SW-enriched pathways were primarily related to electron transport, oxidative phosphorylation, and energy metabolism. Together, these findings indicate that salinity acclimation might shape mitochondrial regulatory responses to cold stress and that SW acclimation is associated with a more tightly regulated mitochondrial response in euryhaline teleosts.