Halicampus grayi, Gray's pipefish, also known as the mud pipefish or spiny pipefish, is a species of marine fish of the family Syngnathidae. It is found in the Indo-Pacific in the Gulf of Aden, Sri Lanka, and from the Gulf of Thailand to Japan, the Marshall Islands, and the Great Barrier Reef. It lives to depth of 100 metres (330 ft), and planktonic juveniles have been found above depths of 3,000 metres (1.9 mi). It occurs in muddy habitats, in estuaries, and on coral reefs, where it likely feeds on small crustaceans. It can grow to lengths of 20 centimetres (7.9 in). This species is ovoviviparous, with males carrying eggs in a brood pouch before giving birth to live young.

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