Parentage assessment of incomplete ossification in larval Japanese flounder by microsatellite DNA markers

Skeletal malformations are a serious problem in seed production of Japanese flounder Paralichthys olivaceus, and genetic effect is sometimes suggested as one of the causative factors. In this study, we examined a skeletal deformity named incomplete ossification, and studied its morphological character and parentage assessment of the deformity by microsatellite DNA markers in the hatchery produced offspring at a commercial farm. Naturally spawned fertilized eggs from flounder broodstocks (eight dams and 19 sires) were introduced into 50 kl tanks and reared with normal procedures. We conducted two lots of seed production with lot 2 started one-week later under the same rearing conditions as lot 1. Deformed and normal individuals were collected at 35 days post-hatch and used for further analysis. Body shape of deformed individuals was narrower than that of normal individuals. Moreover, alcian blue-alizarin red staining revealed that vertebrae and the cranium were partly ossified and the appendicular skeleton and fin rays were not ossified even if those parts were completely ossified in normal individuals. DNA parentage analysis revealed that one dam and sire in lot 1 and a dam and two sires in lot 2 were significantly related to the deformed individuals. The dam and sire significantly related to the deformed individuals were the same in the two lots, even though parentages related to normal individuals were different in the two lots. Our results suggest that this type of deformity of Japanese flounder is caused by incomplete ossification and probably affected by genetic factors. Therefore, pedigree selection will be useful for prevention of this deformity.