Histological Observation of the Spine of the Green Spotted Pufferfish (Dichotomyctere nigroviridis)

Abstract

Since the publication of the draft genome sequence of the green spotted pufferfish (Dichotomyctere nigroviridis), it has become an important model organism for genetic research and is expected to be increasingly used in experimental studies, similar to medaka and zebrafish. We previously reported the structural characteristics of the jawbones and teeth of the green spotted pufferfish. In the present study, we investigated the spines, which are modified epidermal structures analogous in origin to teeth, using stereomicroscopy, light microscopy, and electron microscopy. The spines were pyramidal in shape with a basal portion oriented toward the rostral side, and no regional morphological differences were observed. A depression was present on the dermal side of the basal portion of each spine, into which numerous collagen fiber bundles were inserted, whereas no such depression was noted on the visceral side. The collagen fibers inserted into the dermal side consisted of bundles extending rostrally as well as bundles that reversed direction at the base of the spine and extended caudally. These results suggest that, during inflation of the body, tension generated by these collagen fibers pulls the spines both rostrally and caudally, thereby causing the spines to become erect.