Double-end Pipehorse

The alligator pipefish can grow to a length of about 29 cm (11 in) though a more typical length is 20 cm (8 in). The narrow head has the snout tipped by a pair of short tentacles and the body is elongated and tetrahedral. The dorsal fin has 38 to 48 soft rays and the anal fins have 4 soft rays. The tail is long and tapering. It is prehensile and lacks a tail fin, being used to anchor the fish to vegetation. The colour of this fish tends to match its surroundings and is usually some shade of green, brown, or grey. Females are often blotched and may have a white zigzag line running along the abdomen.

The alligator pipefish occurs in tropical and subtropical parts of the Indian Ocean and Pacific Ocean. Its range extends from South Africa, the East Coast of Africa, and the Red Sea to India, Japan, Indonesia, the Philippines, New Guinea, Australia, and various Pacific Islands. In Australia its range extends from Geraldton in Western Australia around the coast of the Northern Territory and Queensland to Batemans Bay in New South Wales. It occurs in lagoons and on reef flats, in bays and estuaries, in seagrass meadows, and in floating masses of algae, usually at depths of less than 5 m (16 ft).

The alligator pipefish is an inefficient swimmer, moving by an undulating motion of its pectoral and dorsal fins. It feeds on zooplankton and small creatures which it sucks into its mouth. The diet includes amphipods, mysids, shrimps, other benthic invertebrates, and small fish. The alligator pipefish is sexually dimorphic with males being larger than females. Males become mature at a length of about 180 mm (7 in). Breeding takes place during the summer in Moreton Bay, Queensland but occurs at any time of year in Papua New Guinea. A female produces a batch of 60 to 200 eggs which are retained by the male in a brood pouch on his abdomen. Here they remain until they hatch. The male and female seem to have a monogamous relationship with all the developing eggs being at the same stage of development and presumably the product of a single female.