Giant kokopu
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| Giant kokopu | |
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| Giant Kokopu | |
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G. argenteus
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| Galaxias argenteus (J. F. Gmelin, 1789)
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The giant kokopu (Galaxias argenteus) is a species of amphidromous ray-finned fish in the genus Galaxias, found only in New Zealand. It commonly grows to 300–400 mm (12–16 in) in total length, and the longest recorded was 580 mm (23 in)[2] making it the largest member of the family Galaxiidae. It is a mostly lowland species, commonly found in slow-flowing streams, wetlands, lakes, and lagoons.[2] It is has an amphidromous life cycle, with larvae going to sea soon after hatching and returning about four months later as small juveniles, 45–50 mm long.[2] Juvenile giant kokopu form a small part of the annual whitebait catch.[3]
Description
Like all galaxiids, this fish lacks scales and has a thick, leathery skin covered with mucus. The body is very broad, appearing round or square in cross-section, with strong, fleshy fins.[2] The mouth is very large.[2] Giant kokopu are typically olive brown, varying from near-black to pale olive.[2] In adults the body is patterned with pale yellow spots, crescents and lines, markings becoming smaller and more profuse as the fish ages; the patterning begins in juveniles with sparse vertical bars and spots along the lateral line. As the fish grows these markings lengthen and then fade out, while the adult markings fade in.[2][4] Small giant kokopu may be confused with small banded kokopu, but giant kokopu lack a silver mark behind the gills, and their markings never fork or fade out at the top and bottom.[4]
Behaviour
The giant kokopu is primarily a lowland species and its young enter rivers in spring, but it has never actually been observed spawning, and little is known of its reproductive biology. Some fish exist permanently in land-locked stream systems. Adults prefer slow-flowing waters in lowland runs and pools. They usually use cover such as overhanging vegetation, logs, undercut banks, or debris to lurk, awaiting passing prey. Their diet includes aquatic and terrestrial insects, freshwater crayfish (Paranephrops spp.), and spiders.[3]
Status
In 2014, the New Zealand Department of Conservation classified the giant kokopu as "At Risk: Declining" under criterion "B(1/1) - 20,000–100,000 mature individuals, predicted decline 10–50%".[5] Also in 2014, the IUCN rated the giant kokopu as "Vulnerable".[1] Primary reasons for their decline include ongoing drainage of wetlands, drain clearance, and land-use changes, particularly the expansion and intensification of dairy farming.[1]
References
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- David, Bruno O., Closs, Gerard P. andArbuckle, Chris J.(2002) 'Distribution of fish in tributaries of the lower Taieri/Waipori rivers, South Island, New Zealand', New Zealand Journal of Marine and Freshwater Research, 36 4, 797 — 808
External links
- New Zealand native freshwater galaxiid fish, Giant kokopu TerraNature, Auckland 2010
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