Torrentfish

Torrentfish
Torrentfish
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Perciformes
Suborder: Trachinoidei
Family: Cheimarrichthyidae
Regan, 1913
Genus: Cheimarrichthys
Haast, 1874
Species: C. fosteri
Binomial name
Cheimarrichthys fosteri
Haast, 1874

The torrentfish, Cheimarrichthys fosteri, is an amphidromous freshwater fish that is endemic to New Zealand. Torrentfish are well adapted to life in shallow, fast-flowing riffles and rapids. They grow to a maximum of 200 mm (7.9 in) in total length, but more commonly reach 100–120 mm (3.9–4.7 in).[2]

Description

Torrentfish are stocky, with a flattened underside, arched back and a broad, downward-tapering head with eyes set high.[2] The lower jaw is very undercut and is surrounded by a fleshy upper lip[2] – an adaptation for picking invertebrates off the surface of stones. The fins are very robust.[2] The pectoral fins are very large and triangular, angled so that water flowing over them depresses the fish against the substrate, helping them to stay in position in fast-flowing water.[3] The pelvic fins are set underneath the head. The dorsal and anal fins are very long-based, with the dorsal fin extending for nearly half of the body length.[2] The tail fin is short and truncated or slightly forked, suited to sudden burst swimming rather than sustained swimming.[3]

All torrentfish have a similar pattern of five dark stripes on a lighter background.[2] 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.[3] These patterns and colouration camouflage the torrentfish and help it to blend in with its stony habitat.

Habitat

Torrentfish are primarily found in shallow, fast-flowing riffles and rapids.[4] They spend little time actively swimming against the rapids, rather spending their time amongst and beneath the loose gravels and cobbles.[4] They emerge from the rapids at night to feed.[5] They are solitary and benthic, but may be found in high densities where there is a large population.[4] Due to their amphidromous lifecycle, they are found in higher numbers closer to the sea.[4]

Torrentfish are mainly found in gravelly rivers, particularly those with wide, open channels, such as braided rivers.[4] They favour rivers that have highly unstable substrates, as the regular movement of the gravels maintains open gaps around and underneath the stones where the torrentfish take refuge from the fast water.[4] 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 [6]

Life Cycle

Torrentfish are amphidromous, with the fry going to sea after hatching, and returning as juveniles to fresh water where they grow to adulthood.[7] Females are found further upstream than males, up to 235 km from the sea, with a large area of overlap.[2][6] Females migrate downstream over summer and autumn when ripe, and return upstream once spent.[7] 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.[8] The torrentfish is unable to form landlocked populations.[9]

Biogeography

The torrentfish is related to the blue cod, an obligate marine fish, and is one of only two of New Zealand's freshwater fish with local marine origins.[9] All of the other species have Australian freshwater ancestors which arrived in New Zealand via dispersal through the sea.[9] The torrentfish is the only member of both its genus and its family.[10]

Status

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".[11] Also in 2014 the IUCN rated the torrentfish as "Vulnerable".[1] Torrentfish are habitat specialists and requires cool, highly oxygenated, fast-flowing water, and so their primary threats include water abstraction, land-use changes affecting water quality, and climate change.[1] River sedimentation is also a threat, as torrentfish live amongst loose gravels and are less common in waterways with compacted substrate.[1][4]

References

  1. 1 2 3 4 IUCN Redlist of Threatened Species. "Cheimarrichthys fosteri". Retrieved 5 August 2015.
  2. 1 2 3 4 5 6 7 McDowall, R.M. (2000). The Reed Field Guide to New Zealand Freshwater Fishes. Auckland: Reed. ISBN 0 7900 0725 8.
  3. 1 2 3 McQueen, S.; Morris, R. (2013). A Photographic Guide to Freshwater Fishes of New Zealand. Auckland: New Holland. ISBN 978 1 86966 3865.
  4. 1 2 3 4 5 6 7 McDowall, R.M. (1990). New Zealand Freshwater Fishes: A Natural History and Guide. Auckland: Heinemann Reed.
  5. ↑ Glova, G.J.; Sagar, P.M. (1987). "Diel feeding periodicity of torrentfish (Cheimarrichthys fosteri) in two braided rivers of Canterbury, New Zealand". New Zealand Journal of Marine and Freshwater Research 21 (4): 555–561. doi:10.1080/00288330.1987.9516259.
  6. 1 2 McDowall, R.M. (2000). "Biogeography of the New Zealand torrentfish, Cheimarrichthys fosteri (Teleostei: Pinguipedidae): a distribution driven mostly by ecology and behaviour". Environmental Biology of Fishes 58.
  7. 1 2 Scrimgeour, G.J.; Eldon, G.A. (1989). "Aspects of the reproductive biology of torrentfish, Cheimarrichthys fosteri, in two braided rivers of Canterbury, New Zealand". New Zealand Journal of Marine and Freshwater Research 23 (1): 19–25. doi:10.1080/00288330.1989.9516336.
  8. ↑ Smith, J. (2014). Freshwater Fish Spawning and Migration Periods (PDF). Hamilton: NIWA. ISBN 978-0-473-32827-6.
  9. 1 2 3 McDowall, R.M. (2010). New Zealand Freshwater Fishes: An Historical and Ecological Biogeography. Springer. ISBN 978-90-481-9270-0.
  10. ↑ Froese, Rainer and Pauly, Daniel, eds. (2013). "Cheimarrichthys fosteri" in FishBase. February 2013 version.
  11. ↑ Goodman, J.M.; Dunn, N.R.; Ravenscroft, P.J.; Allibone, R.M.; Boubee, J.A.T.; David, B.O.; Griffiths, M.; Ling, N.; Hitchmough, R.A; Rolfe, J.R. (2014). "Conservation status of New Zealand freshwater fish, 2013". New Zealand Threat Classification Series 7.
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