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NEW ZEALAND ECOLOGY |
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NATIVE GALAXIID FISH |
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The banded kokopu Galaxias fasciatus belongs to the Galaxiidae family of the Osmeriformes order. It is endemic to New Zealand, but is not listed as threatened.
Juveniles are good climbers, quite able to move upstream to small tributaries that have a good cover of forest canopy. This provides shade and hiding protection the fish require during the day, and protects their invertebrate food source.
Unlike shortjaw kokopu which prefer native forest cover, the banded species is not so fussy, and will occupy streams in radiata pine forest and other non-native vegetation. |
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The banded kokopu is a most exceptional climber, with the ability to ascend through very steep falls. |
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The most distinguishing feature, and the reason behind the name, is the early development of well defined vertical bands on their sides and over the back. The bands become less prominent towards the front, but remain in the tail area of large adults. Similar bands are also on young giant kokopu but disappear in adults.
Banded kokopu has a similar distribution to the other kokopu, giant and shortjaw, with the difference that banded are concentrated in Northland, Auckland and the Coromandel Peninsula, and shortjaw are absent from the Banks Peninsula, Southland, Stewart Island and the Chatham Islands.
The three kokopu species are sparse south of the East Cape of the North Island, and rare along the east coast of the South Island, possibly because of extensive land development of the Canterbury plains, and the sensitivity of whitebait to suspended sediments, and glacial flour in river catchments extending back to the Southern Alps.
Banded kokopu are primarily a coastal species but will penetrate 180 km inland, up to an elevation of 550m.
Landlocked populations have established at some locations, including the Kaihoka Lakes close to the west coast of northwest Nelson, Lake Hochstetter in Westland, Lake Okataina at Rotorua, and Lake Ototoa on the west side of Kaipara Harbour.
Just like shortjaw kokopu, banded kokopu have the same distinctive dark patch behind the gill openings and above the pectoral fin.
As with all galaxiids it does not have scales, but has a leathery, thick skin covered with mucus. A large rounded single dorsal and anal fin are set back close to the large square caudal fin.
Banded kokopu are cryptic and nocturnal, feeding on terrestrial ants, weta, spiders and beetles that end up in the water course, and invertebrate lavae of caddisflies and mayflies.
Kokopu suffer from the introduction of larger trout introduced to New Zealand for sport fishing. The native fish are unlikely to be found where trout have become well established.
Trout are stronger competitors for food, and prey upon the smaller galaxiids. However, kokopu maintain stronger populations in smaller streams and swamps that cannot support trout. |
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A young banded kokopu Galaxias fasciatus with well defined bands along its' entire body.
Photo Stephen Moore, Crown Copyright © Department of Conservation.
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Whitebait and the migration cycle of diadromous galaxiids
New Zealand's freshwater fish fauna is sparse with 41 native species in 9 families, but unique with the predominance of 24 species of Galaxias and Neochanna genera in the Galaxiidae family.
More than half of the freshwater fish fauna is diadromous, moving between fresh and salt water during their life cycle.
Banded kokopu are the smallest whitebait, but will often mature to a length of 20 cm, and sometimes reach 26 cm. Whitebaiters call them "golden bait" because of their golden colour as whitebait.
The five whitebait galaxiids, banded kokopu, giant kokopu, shortjaw kokopu, inanga and koaro are amphidromous, a particular form of diadromy relating to breeding in freshwater.
Adult galaxiids make their way downstream to rivermouths in the autumn to spawn. Thousands of eggs are laid amongst vegetation on river and stream banks flooded by a spring (very high) tide.
Males fertilize the eggs with such large amounts of sperm (milt) that the water turns milky.
When the tide recedes the eggs sit out of water for two weeks or more remaining moist in the vegetation until the next spring tide, when they hatch and larvae are washed out to sea.
After spending four to five months of winter in the ocean, large shoals of juvenile fish (whitebait), up to 5 cm long and 3 to 4 mm wide, swim into river and stream estuaries on the incoming tide in spring.
They make their way upstream in the final stage of an incredible journey for such a small fish, to develop into adult freshwater fish.
The tiny, almost transparent New Zealand whitebait, caught in a net or screen, are primarily the migratory juveniles of inanga, koaro, and banded kokopu.
Inanga make up the bulk of the whitebait catch in New Zealand, but are not present in sufficient quantities in Australia and South America.
The regulated whitebait season is from mid-August until the end of November throughout most of New Zealand except Westland. Any whitebait catch outside this period is prohibited. There are restrictions on the size of fishing gear, but there is no catch limit.
At different times and in some parts of the country, whitebait runs also include juvenile and adult Retropinna (smelt) and Neochanna (mudfish); juvenile Gobiomorphus (bullies), and Anguilla (eel) species. The whitebait of grayling Prototroctes oxyrhynchus were also in the runs before it became extinct. |
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The ancient Gondwana ancestry of galaxiid fish .....
Only two of New Zealand's 19 Galaxias species are not endemic. Inanga G. maculatus is widespread throughout the southern oceans in Tasmania, southeastern and southwestern Australia, South America, and some Pacific Islands. Koaro G. brevipinnis is found in south eastern Australia and Tasmania.
This is the first indication of a Gondwanan ancestry of galaxiids. The question remains, whether the distribution of galaxiids around the Southern Pacific ocean was by dispersal following the breakup of the Gondwana continent, and separation of the Zealandia continent 80 million years ago; or by vicariance within Gondwana through Antarctica before continental separation.
Dispersal is the migration of an ancestral population across a pre-formed barrier, such as an ocean.
Vicariance is the separation of a population by a barrier, which isolates a new population, and in many cases is the initiation of speciation and the evolution of new species.
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The linked continents of South America, Antarctica, Australia and New Zealand were an overland dispersal route 130 to 35 million years ago. |
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Evidence of a vicariant origin of the New Zealand freshwater fauna is provided by a relationship between Galaxiid fish and tiny parasitic larva of the freshwater mussel, genus Hyridella, called a glochidium.
The larva attach to the fish's gills to obtain nutrients and get a free ride. The minute larval would be washed away in the current without an attachment to the fish.
By coincidence, the mussel family Hyriidae occurs in New Zealand, South America and eastern Australia in the same habitat with galaxiid fishes.
The dispersal of larva to coincide with the galaxiid fish, and evolution of the same relation- ship on different continents, would have been an ecological phenomenon that is hard to imagine. It is easier to accept vicariant separation of populations, when the larva and fish were associated before Gondwana broke up.
An ancient ancestry, Gondwana origin, and vicariant origin of New Zealand freshwater fauna further revolves around the only two species of freshwater crayfish Paranephrops planifrons and P. zealandicus. Crayfish relatives in the Parastacidae family in Australia (yabby), and South America are thought to be of Gondwanan origin.
Another coincidence is a relation-ship between flatworms of the genus Temnocephala that attach to the claws of koura. They only live on a host.
Temnocephala have the same relationship with freshwater crayfish in Australia, and other relatives attach themselves to various hosts, including snails, crayfish and turtles in Brazil, Chile, Argentina, Uruguay, Indonesia and New Guinea.
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