Histological observation of the jaws and teeth of the green spotted pufferfish (Tetraodon nigroviridis)

The green spotted pufferfish (Tetraodon nigroviridis) is a brackish tropical fish whose draft genomic sequence has been published. Its genome is the smallest among vertebrates, and genes account for a high rate of the genome. In addition, many genes have a specific function. Because of these characteristics, the green spotted pufferfish is used as a model animal for genetics. Therefore, this species is likely to be used for basic and clinical studies, similarly to zebrafish and medaka, but no study on its jaw bone and tooth structures has been reported. In this study, we observed the jaw and tooth structures of green spotted pufferfish with an about 3-cm body length using electron and light microscopes. In its jaws, the bilateral bones were joined through finger-like processes at the middle on both upper and lower sides. Several tooth germs in different developmental stages were vertically arranged in the jaw bone, which may have a rod-like morphology in the mesio-distal direction. Soft tissue was present between the tooth germs. A protrusion containing tooth germs was present on the bilateral lingual sides in the upper and lower jaw bones, but the position of this protrusion was lower than the jaw bone apex. Based on these findings, the green spotted pufferfish may be used as an experimental animal useful for studies on tooth morphogenesis.