Identification of Malformation in Juvenile Japanese Flounder (Paralichthys olivaceus) Using External Morphology and Osteological Observation

To construct basis for malformation fish database, hatchery-reared Japanese flounder Paralichthys olivaceus juveniles were sorted out into morphologically normal and abnormal fish using their external morphology and osteological observation. The malformed juveniles were classified into 8 types by their external morphologies, and the skeletal malformed sites were specified 6 out of 8 abnormal types. Total lengths of normal fish, which were judged by their external morphologies, tended to be larger than abnormal fishes. About 90% of normal fish, which were judged by their external morphology, had no skeletal malformed sites from their skeletal preparations. In contrast, the concordance rate of abnormal fishes between external morphology and skeletal observation was about 55%, and about 45% of abnormal fish, which were judged by their external morphology, had no skeletal malformed sites from their skeletal preparations. It is important to construct basis for morphologically abnormal fish database that skeletal normal fish could be accurately sorted into normal fish by external morphology