Hippocampus denise
embryos develop internally over time, the females giving birth to fully formed live young, a process called vivipary.
Seahorses are typically monogamous – during a breeding cycle the male will accept eggs from a single female. Mating occurs after an energetic courtship ritual of colourful, synchronised movement that can last for hours.
Male seahorses have a unique reproductive system: the female transfers her entire clutch of eggs over to the male’ s specialised brood pouch using
Jayakar ' s seahorse Hippocampus jayakari her ovipositor, a tube-like organ that deposits eggs. Additional cool seahorse fact here – eggs cannot be fertilised within the pouch, as there is no internal sperm duct. Anatomically, the spermatozoa must be ejaculated onto the eggs via an external duct when the couple are in close contact. But scientists are still not quite sure when this happens. They speculatively believe that the ovipositor acts like a scoop pushing both sperm and eggs into the pouch.
The pouch seals shut almost immediately( six seconds in some species) after mating and resembles a mammalian uterus, with a vascular placenta-like system inside. This enables aeration( transfer of oxygen), osmoregulation( balancing of salt concentrations) and protection for developing embryos. Throughout pregnancy, the male produces a hormone( prolactin) that nourishes the embryos, while all waste products diffuse out into the male’ s bloodstream via the placenta-like tissue in the pouch.
“ At the end of the pregnancy, males go into labour”
At the end of the pregnancy, males go into labour triggered by the release of gonadotrophins( follicle-stimulating hormones) and an increase in estrogen, taking hours to fully expel the brood of miniature seahorses from his pouch. Once released the young are fully independent, receiving no additional parental care.
There remains no scientific consensus on the evolutionary benefit of pregnancy in male seahorses. One theory is an increase in offspring; if following labour both the male and female are ready to mate again, then multiple broods can be produced by each seahorse couple in a single year. This has great benefits to maintaining or increasing local populations of seahorses.
Seahorse populations are under threat from the aquarium trade and from traditional Chinese medicine, as well as figuring in accidental bycatch. Given such pressures, the ability to raise multiple broods may prove to be vital for their continued survival. �
Spiny seahorse Hippocampus histrix
Hippocampus bargibanti
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