Torrentfish

Torrentfish are stocky, with a flattened underside, arched back and a broad, downward-tapering head with eyes set high. The pelvic fins are set underneath the head. The dorsal and anal fins have very long bases, the dorsal fin extending for nearly half of the body length. The tail fin is short and truncated or slightly forked, suited to sudden burst swimming rather than sustained swimming. All torrentfish have a similar pattern of five dark stripes on a lighter background. There are three stripes on the body, generally angled downwards towards the head, with a fourth stripe vertically at the base of the tail and a fifth passing through the eyes and angling downwards towards the base of the pectoral fin. Their colouration is either dark grey on a lighter grey background, or dark brown on a lighter brown background, changing according to the surroundings of the fish. This colour pattern camouflages the torrentfish and help it to blend in with its stony habitat. ==Habitat==

Torrentfish are primarily found in shallow, fast-flowing riffles and rapids. They spend little time actively swimming against the rapids, living instead amongst and beneath loose gravels and cobbles. Torrentfish are solitary and benthic, but may be found in high densities where there is a large population. ==Life cycle==

Torrentfish are amphidromous: the fry go to sea after hatching, and return as juveniles to fresh water where they grow to adulthood. Female torrentfish are found further upstream than males, up to 235 km from the sea, with a large area of overlap. Because they have to spend time at sea, torrentfish are unable to form landlocked populations like some other New Zealand native fishes. ==Biogeography==

The torrentfish is related to the blue cod, an obligate marine fish, and is one of only two New Zealand freshwater fish with local marine origins. ==Conservation==

In 2014 the New Zealand Department of Conservation classified the torrentfish as "At Risk: Declining" with the qualifier "C – very large population and low to high ongoing or predicted decline". Also in 2014 the IUCN rated the torrentfish as "Vulnerable". Torrentfish require a specialised habitat with cool, highly oxygenated, fast-flowing water, and so are threatened by water being taken for irrigation, water pollution, and climate change. River sedimentation is also a threat, as torrentfish need to live amongst loose gravels and are less common in waterways with compacted substrate. ==References==