The male is the one with a pouch in front, where he carries the eggs:
"Sea horse males are the only male animals capable of giving birth. The female will deposit her eggs into the male's abdomen. The male fertilizes them, and then the embryos will attach themselves into the male's pouch. Here he will nurture the embryos, delivering oxygen and removing waste. As if this wasn't taxing enough, he will then go into a painful labor, whereby his color will drain, becoming pasty in appearance. The exhausting contractions will leave him spent after pushing up to nearly 200 sea horses out of his body. No sooner is he done giving birth, that some males will begin to show off their pouch, wanting to become impregnated again!" 
The Wiki Article:
The male seahorse is equipped with a brood pouch on the ventral, or front-facing, side. When mating, the female seahorse deposits the eggs in the male's pouch, which the male then internally fertilizes. The male carries the eggs until they emerge, expelling fully-developed, miniature seahorses in the water.
|Includes CC-BY-SA content from Wikipedia's Seahorse article (authors)|