Abstract
Twin-tail ornamental goldfish have a bifurcated caudal fin with a morphology that is extremely diverged from the conventional body plan of the vertebrates. Here, we investigate the muscu-loskeletal histology of this bifurcated caudal fin. From some of the investigated twin-tail goldfish, we found a twin-tail goldfish specific muscle (hereafter referred to as the “medial caudal muscle”) between left and right bifurcated caudal fin skeletons. Our immunohistochemical analyses revealed that the medial caudal muscle showed laterally biased distribution patterns of the slow and fast muscle fibers. Similar distribution patterns were also commonly observed in several deep muscles of wild-type goldfish as well as zebrafish, suggesting that these muscle fiber distribution patterns are formed by the same molecular developmental mechanisms even though their morphologies are highly diverged. These findings provide empirical evidence to consider how the histological features of a newly emerged morphology are influenced by selective pressures and pre-existing developmental mechanisms.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Revision Comments: We have made the following revisions based on new findings and further analysis: 1. Added immunohistological observations from Oranda specimens, now presented as Figure 8. Accordingly, we revised the description in the subpart on Twin-tail ornamental goldfish in the Results section. 2. New immunohistological observations obtained from the lab strain in 2024 have been incorporated. The results from The 24 twin #01 are now presented as Figure 13, and those from The 24 twin #02 as Figure 14. 3. The descriptions of these new results have been added to the subpart on chdS mutant lab strain progenies in the Results section. 4. Since the results from The 24 twin #01 showed a different slow muscle fiber distribution compared to other specimens, we have added a discussion of this interpretation in the Selective pressures and developmental mechanisms section of the Discussion. Significant revisions have been made to this part. 5. To explain the results from The 24 twin #01, we also revised the schematic diagram in Figure 15.
