Developmental neuroanatomy of the Rosy Bitterling Rhodeus ocellatus (Teleostei: Cypriniformes)--A microCT study

Bitterlings are a group of teleost fish (Cyprinifromes: Acheilanathidae) notable for their brood parasitic lifestyle. Bitterling embryos develop as parasites inside the gill chamber of their freshwater mussel hosts. However, little is known about brain development in this species. Here, we have imaged the development of the brain of the Rosy Bitterling (Rhodeus ocellatus) at four embryonic stages (165, 185, 210, 235 hours post-fertilization) using micro-computed tomography (microCT) with special emphasis on developmental regionalization and brain ventricular organization. We provide a detailed neuroanatomical account of the development of the brain divisions with reference to The Atlas of Early zebrafish Brain Development and the updated prosomeric model. Segmentation and three-dimensional visualization of the ventricular system were performed in order to clarify changes in the longitudinal brain axis as a result of cephalic flexure during development. During early embryonic and larval development, we find that histological differentiation, tissue boundaries, periventricular proliferation zones, and ventricular spaces are all recognizable using microCT. Importantly, our approach is validated by the fact that the profile of CT values displayed here in the bitterling brain are consistent with genoarchitecture identified in previous studies. We also find developmental heterochrony of the inferior lobe in the Rosy Bitterling compared to the zebrafish. Our study provides a foundation for future studies of the brain development in the Rosy Bitterling, a valuable model species for studying the evolutionary adaptations associated with brood parasitism.