MORPHOLOGICAL STUDIES ON THE DEVELOPMENT OF MELANOPHORES AND SCALES IN MALPIGMENTED PARALICHTHYS OLIVACEUS

In this study,integrated morphological observations were carried out on the occurrence and development of melanophores and scales in hatchery-reared normal and malpigmented Japanese flounder Paralichthys olivaceus. The results showed that starry larval melanophores occurred first on the skin of both sides of larvae.With the process of metamorphosis,on the ocular side(left side),adult melanophores occurred and replaced larval melanophores gradually,while on the blind side (right side),larval melanophores degenerated and no adult melanophores appeared.The blind side lost pigment gradually and became white in the end.Malpigmentation occurred at the post-metamorphosis stage.Albinism and ambicoloration formed almost at the same time.Due to unsuccessful replacement of adult melanophores by larval melanophores,the skin in ocular side of fish body lost pigment and formed white irregular patches.Albinism occurred.On the other hand,adult melanophores developed abnormally and replaced the larval melanophores and eventually formed dark patches on the blind side.It was called ambicoloration.At 30 days old,the malpigmentation became evident at the completion of metamorphosis.At about 60 days old,original cycloid scales occurred on both sides of larval bodies.The cycloid scales developed into ctenoid scales on the normal ocular side while remained original status on the normal blind side.Contrast to malpigmented individuals,it was observed that the albino ocular side was still covered by cycloid scales,but the cycloid scales developed into ctenoid scales on the ambicolored blind side.Furthermore,observations of the scales on different postions of recovering albino fish showed the development of scales from immature cycloid scales to mature ctenoid scales following the recovery of pigmentation.It is suggested that a close relationship existed between the occurrence of pigmentation and development of scales in Japanese flounder.