Postembryonic staging of wild-type goldfish, with brief reference to skeletal systems

Background: Artificial selection of postembryonic features is known to have established morphological variation in goldfish (Carassius auratus). Although previous studies have suggested that goldfish and zebrafish are almost directly comparable at the embryonic level, little is known at the postembryonic level. Results: Here, we categorized the postembryonic developmental process in the wild-type goldfish into 11 different stages. We also report certain differences between the postembryonic developmental processes of goldfish and zebrafish, especially in the skeletal systems (scales and median fin skeletons), suggesting that postembryonic development underwent evolutionary divergence in these two teleost species. Conclusions: Our postembryonic staging system of wild-type goldfish paves the way for careful and appropriate comparison with other teleost species. The staging system will also facilitate comparative ontogenic analyses between wild-type and mutant goldfish strains, allowing us to closely study the relationship between artificial selection and molecular developmental mechanisms in vertebrates.