Comparative study of the histology and Micro-CT scan of the goldfish hood

The hood (also known as head growth or wen) is a distinctive feature of goldfish characterized by skin tissue proliferation. The classification of goldfish hood types and the study of the underlying skeletal structure still have substantial gaps in research. This study aimed to investigate the structural differences in goldfish hood tissues using histological and Micro-CT comparisons, based on traditional Chinese classifications. Histological observations revealed two distinct types: the one-piece type (Crown Pearlscale), characterized by a uniformly thickened epidermis, and the fused type (Oranda, Red Cap Oranda, and Ranchu), which showed irregular epidermal extensions into the dermis. Micro-CT scans further demonstrated that hooded goldfish exhibited skull protrusions, bone spurs, and widening of the cranial region. These findings indicate that fibroblast activity, tissue edema, and bone structural changes may be key drivers of hood formation in these goldfish varieties.