The big-belly seahorse has a forward-tilted, long-snouted head, distended but narrow pot belly, and a long coiled tail. It swims using its dorsal fin with a vertical stance – when not swimming it coils its prehensile tail around any suitable growth, such as seaweed, waiting for planktonic animals to drift by when they are sucked up by the small mouth set at the tip of the snout much like a vacuum cleaner. Seahorses are voracious feeders, eating mainly crustaceans, such as shrimps, and other small animals living among the seaweed such as copepods and amphipods. They do not masticate so they can eat to excess because of their small gut tract. Each eye moves separately making it easier for them to see food and predators.
It is quite easy to distinguish males from females. The male have a smooth soft pouch-like area at the base of its abdomen between where the stomach meets the tail on the front side. Males also have a fin here but it is less obvious. The female will have more of a pointed stomach with a very obvious fin at the base of the stomach.