Abstract
To understand genetic factors affecting observed deformities in the head regions of artificially raised red sea bream, we evaluated morphological features of deformed fish at 60 days post-hatching. The incidence of deformities in the head region was 3.4%, and included cases featuring twisted lower jaws, lack of an upper jaw fragment, pugheadness and shortened lower jaws. The highest incidence of deformity was a shortened lower jaw, and as a direct consequence, we focused upon individuals exhibiting a shortened lower jaw for further genetic analysis. Genetic assessment based on microsatellite DNA markers was conducted in order to evaluate the genetic cause of the shortened lower jaw deformity. There were no obvious differences in heterozygosity or allele frequencies between individuals exhibiting normal and shortened lower jaws. DNA parentage analysis indicated that normal individuals were generated from 9 dams and 16 sires, and 43 parental pairs were observed. Shortened lower jaw individuals were generated from 9 dams and 15 sires, and 40 parental pairs were observed. No broodstock generated a significant numbers of individuals with a shortened lower jaw. Our results suggest that the shortened lower jaw individuals assessed in this study had arisen via environmental factors rather than genetic factors.
