Meeting Abstract
Seahorses are unique in mode of reproduction, i.e., male, not female, carries embryos in a brood pouch located on the ventral surface of the tail. In order to study how the brood pouch is formed during the development of male seahorses from juvenile to adult, we made histological observations of various stages of brood pouch development. First, brood pouch of mature male was observed by hematoxylin-eosin stain, Masson trichrome stain, and reticulin silver stain. As results, the brood pouch was composed of internal epithelium called “pseudoplacenta”, dermis layer and surface epithelium from inside to outside. The dermis layer contained dense connective tissues indicated by blue color with Masson trichrome stain. The “pseudoplacenta” contained loose connective tissues indicated by black color with reticulin silver stain. These results suggest that the dermis layer is mainly composed of collagen fibers, while the “pseudoplacenta” is mainly composed of reticular fibers. A lot of mucus cells were observed in the surface epithelium, while few were in the internal epithelium. Next, brood pouch formation process was observed. In juvenile male seahorse, the dermis of both sides of body seemed to rise and elongate toward the midline of the body. At the beginning, the pouch was only composed of dermis. As development proceeded, smooth muscle in dermis layer and “pseudoplacenta” were differentiated. The “pseudoplacenta” appeared to be formed from the dorsal parts of the pouch, and finally surrounded the pouch. At the beginning, there were no remarkable morphological differences between internal epithelium and surface epithelium, and the mucus cells were observed in the both epithelia. As development proceeds, the number of mucus cells decreased in the internal epithelium, and finally few mucus cells appeared to be observed in mature seahorses.
