Cortisol analysis in market-frozen rainbow trout (Oncorhynchus mykiss)

Stress reactions are common in the ability of animals to cope with various conditions. Cortisol, a stress biomarker, is effective for evaluating acute and chronic stress in animals. We hypothesized that fish suffering from stress have higher stress levels during growth, which is reflected in higher cortisol levels in the body matrices. Elevated cortisol levels in frozen fish meat may reflect the cumulative stress experienced throughout the farm to market process. Therefore, this study aimed to validate a cortisol measurement method in frozen fish meat as a potential indicator of retrospective stress exposure and meat quality. Sixteen frozen rainbow trout (Oncorhynchus mykiss) samples (mean weight: 362 ± 95 g) were purchased from a single farm in Korea. Cortisol levels in adipose, anal, pelvic, pectoral, dorsal, and caudal fins of fish samples were analyzed using a competitive enzyme immunoassay. Significant differences (p < 0.05) were found between the different fin types in the five fish samples and among the 16 individual caudal fin samples. This pilot study demonstrates the feasibility of cortisol assessment in market-available fish meat, providing a method for the pre-harvest assessment of fish welfare and meat quality with the potential to improve aquaculture quality control and consumer confidence.