Histological study of deformity in eye location in Japanese flounder Paralichthys olivaceus

Abstract

The internal structure of malformed Japanese flounder Paralichthys olivaceus juveniles in eye location was histologically examined and deformed bones were identified as the tissue important for eye relocation. A deformed pseudomesial bar (Pb) was the common feature for individuals with abnormal eye location (AEL individuals). Individuals with mild AEL had undeveloped Pb and those with serious AEL had no Pb or two Pb on both sides. When the Pb was absent, left-right asymmetry of the other hard tissues in the head region was disordered. For these reasons, Pb was considered important for eye relocation, and the possibility to define the left-right asymmetry of other tissues was suggested. The skin beneath the right eye and just outside the Pb is thickened in all normal individuals, while this skin was not thickened in most Pb-absent individuals, suggesting the possibility of the presence of upper control of Pb formation by the skin.