겨울신호 처리가 대서양연어(Salmo salar)의 스몰트화 및 아가미 이온 조절기전에 미치는 분자생리학적 영향 = Molecular and physiological effects of an artificial winter signal on smoltification and gill ion regulatory mechanisms in Atlantic salmon (Salmo salar)

다국어 초록 (Multilingual Abstract)

Continuous light (24L:00D) is widely adopted in recirculating aquaculture systems (RAS) to maximize Atlantic salmon growth; however, it often induces early maturation and disrupts normal smoltification. This study investigated the physiological and molecular effects of an artificially winter signal on the smoltification process. Atlantic salmon were subjected to three photoperiod regimes for 22 weeks: 12L:12D (12L), 24L:00D (24L) and a winter signal (WS; 24L for 11 weeks, followed by 12L for 4 weeks, and returning to 24L for 7 weeks). Morphologically, the WS group exhibited a significant increase in the smolt index from week 15 onward, characterized by the complete parr marks loss and pronounced silvering. Physiologically, this group demonstrated the highest gill Na+/K+- ATPase (NKA) activity by week 22. Molecular analyses revealed successful isoform switching within the gills of the WS group, highlighted by the downregulation of freshwater-type ion transporter genes (NKAα1a and NHE) and the upregulation of seawater-type genes (NKAα1b and CFTR). The NKAα1b/NKAα1a ratio, a critical molecular indicator for smoltification, progressively increased in the WS group, reaching a level 15.64-fold higher than that of the 24L group by the end of the trial. In contrast, the 24L group maintained elevated expression levels of freshwater-type genes, indicative of incomplete smoltification. These findings suggest that an appropriate WS serves as an indispensable environmental stimulus for triggering the functional and structural remodeling of gill ionocytes, suggesting the completion of pre-adaptive physiological preparedness for seawater entry. Consequently, our findings provide fundamental data for optimizing photoperiod management strategies to produce high-quality smolts in RAS.