Measuring cortisol in fish scales to study stress in wild tropical tuna

Cortisol is recognized as a physiological indicator of stress in fish. However, this hormone typically measured plasma samples. In study, cortisol content was evaluated for the first time scales tropical tuna. The sample included 20 skipjack tuna (Katsuwonus pelamis) and 25 yellowfin (Thunnus albacares) collected Atlantic (the Gulf Guinea off Ivory Coast) Indian Ocean (off Reunion Island), their were analyzed using an ELISA test. results indicated that on average, concentration (1) did not show any geographical pattern, (2) independent fish size, (3) significantly higher (mean 4.75 ± 6.56 ng g?1) than 1.65 1.85 g?1), although difference mainly due to four individuals. Larger datasets would be needed confirm species concentration. particularly high observed individuals may from different schools, suggesting need future sampling free-swimming schools investigate intra- inter-school variability This study opens door research, including collection tagged individuals, links between chronic behavior these species.