seahorse

Like all other fishes, seahorses uses their gills for breathing.
Please see:
http://www.aquarium.org/seahorses/f-faq.htm
What is a seahorse, anyway?

圖片參考：http://www.aquarium.org/seahorses/faq_pic1a.jpg
Seahorses are truly unique. Unlike their hoofed namesakes, seahorses have all the necessary parts of a fish: fins for swimming, gills for breathing, and a swim bladder for keeping them afloat. Seahorses differ from their fishier relatives by having an upright posture; a long, tube-shaped snout and a prehensile tail for grabbing hold of plants and corals. Their jaws are sealed together with just a small opening at the end for sucking in food.
Hope it helps.

seahorses uses gills for breathing.