Formation of seahorse brood pouch
Brood pouch
Seahorses are teleost fish and have a unique morphology.?The female body is completely covered with bony plates. So, their body looks rugge. On the other hand, males have a soft part called a brood pouch, that is not covered with bony plates. The most unique point is that male seahorses get pregnant. ? Once the male seahorse receives eggs from the female, the male fish protects the embryos within the brood pouch, and later gives birth.?
Observation of brood pouches throughout the development of seahorses
The brood pouch is a characteristic organ of adult males, but the pouch is not yet formed in juvenile fish. ? We observed the tail region just posterior to the cloaca throughout the formation of the brood pouch. ?As the first step of brood pouch formation, a white plate-like primordium was formed. ?Both sides of the primordium then elongate toward the midline. ?When it reached the midline, it fused from the caudal side. ?Finally, fusion stopped, and a sac-like brood pouch with an entrance was formed.
Histological observation of the brood pouch
At the early stages of brood pouch formation, the pouch seems to be composed of a uniform dermal layer.?After that, inner layer called "placenta" was observed from the dorsal side of the brood pouch. ?In addition, smooth muscle can be observed from the middle of the dermis layer. ?
Summary
The primordium of the brood pouch first appears at the ventral side of the tail. ? Then, the dermis elongates toward the midline of the body to form a sac-like structure. Next, the placenta appears from the dorsal side of the lumen and covers the lumen entirely, ready to incubate embryos. ?
Original Paper
Mari Kawaguchi, Ryohei Okubo, Akari Harada, Kazuki Miyasaka, Kensuke Takada, Junya Hiroi, and Shigeki Yasumasu (2017) Morphology of brood pouch formation in the pot-bellied seahorse Hippocampus abdominalis. Zoological Letters, 3: 19.
DOI: 10.1186/s40851-017-0080-9