Studies on morphological abnormalities in hatchery-reared three-lined tonguefish Cynoglossus abbreviatus

Measurements and observations of juvenile hatchery-reared three-lined tonguefish Cynoglossus abbreviatus were performed to examine morphological abnormalities, focusing on five asymmetric characters: eye position, body coloration, presence of a nasal tube, presence of dentition, and premaxillary length. Hatchery-reared juveniles were classified into a normal type similar to wild fish, an ambicolored type (with eyes on both sides of the body), and an intermediate type showing characteristics between the other two types. The ambicolored and intermediate types are considered metamorphosis-related malformations of flatfishes. Pseudoalbinism and reversal, which are commonly observed in hatchery-reared flatfishes, were not found in this study. The most significant result of the present study on hatchery-reared three-lined tonguefish is that the eye position and body coloration of the intermediate-type individuals were between the normal and ambicolored types. Eye migration and body coloration on the blind side of the intermediate type did not synchronize.