Fish vocalization and diel variation patterns of Pacific cod (Gadus macrocephalus) and bluefin gurnard (Chelidonichthys kumu) were investigated using passive acoustic monitoring at a sea-cage facility off Tongyeong, Korea. Autonomous recordings were collected from February 3 to 15, 2023 (Pacific cod) and from September 19 to October 2, 2025 (bluefin gurnard). Power spectral density (PSD) was used to quantify spectral structure and diel variability, and pulse-based grunt detection was applied to time vocal events. For both species, dominant spectral energy occurred below 1 kHz, concentrated at 0.1 – 0.5 kHz for Pacific cod and 0.1 – 0.8 kHz for bluefin gurnard. Pacific cod exhibited a pattern of consistently increasing acoustic activity throughout the night. Bluefin gurnard activity was primarily restricted to approximately 2 hours after sunset and sunrise, exhibiting relatively low chorus signals. The SPL were approximately 107-125 dB re 1 μPa for Pacific cod and approximately 103 – 110 dB re 1 μPa for bluefin gurnard. Based on the diel variation pattern, high-activity (22:00 – 06:00 KST) and low-activity (10:00 – 18:00 KST) phases were defined, and empirical probability density profiles summarized frequency-dependent distribution shifts between phases. The acoustic characteristics and diel variation patterns of the two fish species' sounds will help manage fishery resources and identify spawning and fishing grounds.