On the anomalous greyish colouration of the blackbelly rosefish Helicolenus dactylopterus (Scorpaeniformes: Scorpaenidae)

Abnormal pigmentation in fish has received much attention from ichthyologists in recent decades. The capture of specimens of the bluemouth Helicolenus dactylopterus with abnormal greyish skin colouration is reported. The specimens were caught by bottom trawling on the Porcupine Bank (west of Ireland, north-eastern Atlantic) in 2023. Depigmented specimens lacking the typical pinkish-red colouration were observed in all juveniles up to approximately 5 cm and in one adult of 18 cm in total length. While the occurrence of this colouration pattern in small specimens is attributed to ontogenetic changes, the unusual colouration in the adult specimen is probably due to a mutation in the carotenoid metabolic pathway. This finding may open new avenues for the study of mutations related to carotenoid metabolism in fish.