The big-belly seahorse is one of the largest of all seahorses, growing up to 35 cm in length (2) (4). Like other seahorses, the head is held at right angles to the body, the eyes can move independently of each other, and the tail is prehensile. Instead of having scales, as most other fish, seahorses have a layer of skin stretched over bony plates that are visible as rings passing around the trunk. Swimming is powered by the rapidly oscillating dorsal fin, and they steer using the fins on either side of the body (the pectoral fins) (9). As the common name suggests, this species has a large swollen belly (4). In common with most other species of seahorse, the big-belly seahorse is well camouflaged; individuals may be brown, yellow, grey, white, orange or mottled, with dark spots and blotches on the head and trunk, and the tail often has alternating pale and dark bands (2). Males differ from females in that they have longer tails, a shorter, more robust snout and more dark markings (4), they also typically have a yellow mark close to the top of the brood pouch (2).