Evaluation of Overwintering Performance of Threeline Grunt (Parapristipoma trilineatum) in Sea Cages Along the Southern Coast of Korea

To evaluate the overwintering performance of threeline grunt (Parapristipoma trilineatum), field experiments were conducted on 3000 subadults and 5000 juveniles reared in sea cages along the southern coast of Korea (SC group), and 600 subadults and 700 juveniles reared in inland tanks on Jeju Island (IT group), under thermally suitable overwintering conditions. Fish were sampled from January to April. The SC group maintained acceptable survival rates of 77.2% in subadults and 75.8% in juveniles. Body weight and standard length in the SC group did not significantly change during overwintering; condition factor and hepatosomatic index varied at specific sampling points. The SC group juveniles exhibited lower plasma glucose levels than the IT group ones. Overwintering in sea cages influenced body composition, characterized by reduced crude protein and increased crude lipid content. Plasma cortisol levels in the SC group juveniles increased significantly in January, whereas hepatic heat shock protein-70 levels showed no distinct changes. Principal component analysis revealed no clustering among groups. Physiological variations in the SC group reflected seasonal adaptation, evidenced by stable survival and no strong coordinated changes among physiological responses. These findings highlight the potential of threeline grunt to overwinter in sea cages along the southern coast of Korea.