Embryonic and postembryonic development of the ornamental twin‐tail goldfish

Abstract

Background Twin‐tail ornamental goldfish have “bifurcated median fins,” a peculiar morphology known to be caused by a mutation in the chdA gene. However, several ambiguities regarding the development of the phenotype remain due to a paucity of detailed observations covering the entire developmental timeframe. Results Here, we report a detailed comparative description of embryonic and postembryonic development for two representative twin‐tail ornamental goldfish strains and single‐tail common goldfish. Our observations reveal a polymorphic developmental process for bifurcated median fins; disrupted axial skeletal development at early larval stages; and modified bilateral location of the pelvic fin. Conclusions Variations in development of bifurcated median fins and disrupted axial skeletal patterns reflect how artificial selection for adult morphological features influenced molecular developmental mechanisms during the domestication of twin‐tail ornamental goldfish. The polymorphic appearance of bifurcated median fins also implies that, unlike previously proposed hypotheses, the development of these structures is controlled by molecular mechanisms independent of those acting on the pelvic fin. Our present findings will facilitate further study of how modifications of preexisting developmental systems may contribute to novel morphological features. Developmental Dynamics 248:251–283, 2019. © 2019 The Authors. Developmental Dynamics published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

Stages of embryonic development in the live‐bearing fish, Gambusia holbrooki

“…Therefore, accurate staging required the use of additional features and indices such as brain partitioning, formation of optic bud and OVC. 17,22,34 The development of the brain rudiment and optic bud were comparable to those reported for zebrafish. 17 Unlike the application of OVC in goldfish 22 and OVL in zebrafish 17 to stage pharyngula, they were more useful for staging segmentation in G. holbrooki.…”

“…Maintaining a uniform temperature is vital for standardization of development. 17,23,32,34 (2) To account for the timing of fertilization, mating was used as a proxy as suggested for G. affinis. 2 In platyfish and swordtail, the duration of gestation is 28 days and mature ova can be fertilized after 7 days.…”

“…This allowed reproducibility and distinction of intermediate developmental stages. 23,26,32,34 Specifically, sequential numeric labeling of the stages with period-specific prefixes, allows easier recognition of chronology as well as development periods. The OVC, 22 the CFRE, 32 CFR, and the HR (bpm) indices were successfully adopted for the first time to define stage characteristics in developing embryos of G. holbrooki.…”

“…Similar inflation of the swim bladder prior to swimming is also known to occur in tilapia 32 and perch. 26 The mouth opening with first peristaltic undulations 22,26,34 and formation of the teeth at parturition suggest that the digestive system is morphologically complete. The pattern of tooth development successively from the "dental determinant" is similar to those observed in zebrafish, 75 cichlids, 76 sticklebacks, 77 and salmonids.…”

Pleiotropic functions of chordin gene causing drastic morphological changes in ornamental goldfish

“…More specifically, at the late larval stages, dorsal fin rays were not observed in group 1 individuals, dorsal fin rays were missing at several body levels in group 2 individuals, and dorsal fin rays were completely developed in the group 3 individuals (Fig. 3i-n) 16,21 . This concordance of phenotypes suggested that chdS wt mRNA at the early embryonic developmental stage influences the eventual skeletal morphology of the dorsal fin (Fig.…”