Ocean acidification (OA) affects the physiological and behavioral traits of marine fish, raising concerns about how wild species will adapt to elevated pCO₂ levels. Using natural volcanic pCO₂ vents at White Island, New Zealand, as analogs for future OA, we sequenced the brain transcriptomes of four highly site-attached fish species from both CO₂ vents and nearby control sites with ambient pCO₂. Notably, the common triplefin (Forsterygion lapillum) exhibited a higher population density in CO₂ vents compared to control sites. Our findings revealed that all species showed significant expression changes in genes related to circadian rhythms, visual perception, energy metabolism, and stimulus responses. The common triplefin demonstrated the largest number of differentially expressed transcripts, particularly in genes related to circadian rhythm and visual perception, which also influence circadian entrainment. In this species, changes in calcium signaling were linked to behaviours (pain response and locomotion behaviors), growth, and reproduction, potentially explaining their success in elevated pCO₂ environments. Furthermore, the common triplefin exhibited positive selection signals in genes associated with circadian entrainment, calcium signaling, pH regulation, and energy metabolism compared to the other three species. These findings suggest that the common triplefin may possess enhanced adaptive traits, enabling it to thrive under future ocean acidification conditions. Our study offers new insights into the potential resilience of marine fish to OA and highlights key molecular pathways that could be targeted for conservation efforts.

Gene expression change,Marine fish,Environmental change,Population size,Wild fish resources