The torrentfish (''Cheimarrichthys fosteri''), or panoko (

Māori Māori or Maori can refer to: Relating to the Māori people * Māori people of New Zealand, or members of that group * Māori language, the language of the Māori people of New Zealand * Māori culture * Cook Islanders, the Māori people of the Co ...

), is an

amphidromous Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousan ...

freshwater fish that is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...

. Torrentfish are well adapted to life in shallow, fast-flowing

riffle A riffle is a shallow landform in a flowing channel. Colloquially, it is a shallow place in a river where water flows quickly past rocks. However, in geology a riffle has specific characteristics. Topographic, sedimentary and hydraulic indica ...

s and

rapid Rapids are sections of a river where the river bed has a relatively steep gradient, causing an increase in water velocity and turbulence. Rapids are hydrological features between a ''run'' (a smoothly flowing part of a stream) and a ''cascade'' ...

s. They grow to a maximum of in

total length Fish measurement is the measuring of individual fish and various parts of their anatomies. These data are used in many areas of ichthyology, including taxonomy and fisheries biology. Overall length * Standard length (SL) is the length of a fish ...

, but more commonly reach .

Description

Torrentfish are stocky, with a flattened underside, arched back and a broad, downward-tapering head with eyes set high. The lower jaw is very undercut and is surrounded by a fleshy upper lip – an adaptation for picking invertebrates off the surface of stones. The fins are very robust. The pectoral fins are very large and triangular, angled so that water flowing over them presses the fish against the riverbed, helping them to stay in position in fast-flowing water. 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

s and

rapids Rapids are sections of a river where the river bed has a relatively steep gradient, causing an increase in water velocity and turbulence. Rapids are hydrological features between a ''run'' (a smoothly flowing part of a stream) and a ''cascade' ...

. They spend little time actively swimming against the rapids, living instead amongst and beneath loose gravels and cobbles. They emerge from the rapids at night to feed. Torrentfish are solitary and

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning " ...

, but may be found in high densities where there is a large population. Because part of their life cycle is spent in the sea, they are found in higher numbers near the coast. Torrentfish are mainly found in gravelly rivers, particularly

braided river A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, ''aits'' or ''eyots''. Braided streams tend to occur in rivers with high sediment ...

s with wide, open channels. They favour rivers with highly unstable substrates, as the regular movement of the gravels maintains open gaps around and underneath the stones where the torrentfish can take refuge from fast water. Although they are strong swimmers, they are poor climbers and are only found far inland if the gradient is low and there are no barriers.

Life Cycle

Torrentfish are

: 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. Females migrate downstream over summer and autumn when ready to lay eggs, and return upstream once spent. It is likely that they spawn in the lower reaches of waterways. Fry hatch and migrate to sea in late summer and autumn, returning a short time later in late autumn and winter. 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. All of the other New Zealand freshwater species have Australian freshwater ancestors which arrived in New Zealand via dispersal through the sea. The torrentfish is the only member of both its

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

and its

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Conservation

In 2014 the New Zealand

Department of Conservation An environmental ministry is a national or subnational government agency politically responsible for the environment and/or natural resources. Various other names are commonly used to identify such agencies, such as Ministry of the Environment ...

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 The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

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

External links

* Torrentfish discussed on RNZ ''Critter of the Week''
10 March 2017
{{Taxonbar, from=Q138392 * Trachiniformes Endemic freshwater fish of New Zealand Fish described in 1874 Taxa named by Julius von Haast