Muscle quality classification in Atlantic cod (Gadus morhua L.) – evaluating Fulton’s condition factor and hepatosomatic index thresholds as quality indicators

Muscle quality in Atlantic cod (Gadus morhua L.) is closely linked to the fish’s nutritional status and energy reserves. Reliable and easy-to-implement indicators are needed to monitor fish condition and prevent quality deterioration during live storage, or in traditional fisheries to facilitate production planning. This study examined the relationship between muscle quality and condition indices in cod exhibiting or lacking signs of severe emaciation (gelatinous texture and atypical white muscle colour) and evaluated whether the derived threshold values for Fulton’s condition factor (K-factor) and hepatosomatic index (HSI) can predict muscle quality across three independent trials. K-factor was calculated using both total body weight (KTW) and somatic weight (KSW) to account for variation in visceral mass. Using data from a controlled feed-deprivation trial, we identified threshold values for KTW, KSW and HSI that distinguish between poor, intermediate, and good-quality fish. When these threshold values were applied to independent trials, the KSW-factor yielded the most consistent and accurate predictions of fillet defects, whereas thresholds for KTW-factor and HSI provided less reliable predictions of muscle quality. These findings demonstrate that simple biological indices, particularly KSW, can support proactive quality management in live storage systems and conventional supply chains. Future work should validate thresholds across seasons and integrate automated measurement technologies.