Comparison of Meristic Variations and Bone Abnormalities between Wild and Laboratory-Reared Red Sea Bream

Abstract

To obtain basic information for the production of healthy and vigorous larvae and juveniles, a comparative study on meristic variations and bone abnormalities between wild and laboratory-reared red sea bream, Pagrus major, was undertaken. Although 95% of the specimens of wild juveniles had a definite number of dorsal fin rays, reared juveniles exhibited extensive variations, and the latter had fewer pectoral fin rays than the former. Bone abnormalities included the transformation of spines to soft rays, shrinkage of lower jaw, pug-headness, shrinkage of anterior centra, fusion of vertebrae, abnormal pterygiophores, etc. Detailed observations of cleared and double-stained specimens revealed that wild juveniles had an average of 0.2 abnormal bones per specimen, whereas, the reared ones had an average of 2.04-21.4 abnormal bones per specimen, depending on the groups. Therefore, reared fishes showed many abnormalities, although they appeared to be normal based on external observation. The causes of these abnormalities have not been elucidated, except for the lordosis. Abnormalities of reared fishes seemed to affect bones and cartilage as well as other tissues, such as the deformity of the inter-nostril epidermis in one case. It is likely that various defects associated with rearing conditions induce a variety of abnormalities. Aquaculturists should attempt to produce larvae and juveniles which are similar in morphological, behavioral, physiological and biochemical characteristcs to wild ones.