The small fish caught each spring by whitebaiters all around the country are actually the juveniles of five species of fish. These five are part of a group of fish called galaxiids (so called because of the patterns of their skin which look like a galaxy of stars) of which there are 20 species, the rest of which don't migrate.
Those that escape the whitebait net grow into silvery, slender adults (about 9 cm long). They spawn in streamside vegetation, even rank exotic grasses are suitable.
Although galaxiid species are found in many places in the Southern Hemisphere, the giant, shortjaw and banded kōkopu only exist in New Zealand.
Our galaxiids are generally nocturnal and very good at hiding. They love bushy streams, where they find both shelter and food, with a rain of insects falling from the overhanging plants.
The main breeding season for our galaxiids is autumn. Inanga migrate downstream to estuaries and lay their eggs among plants and grasses, whereas kōaro and kōkopu stay where they are and lay their eggs on leaf litter and forest plants.
The eggs stay out of water for several weeks, and need good plant cover to keep moist. They hatch when re-immersed, either by spring tides (for inanga) or floods (for kōaro and kōkopu). The larvae then float out to sea where they live and grow over winter, migrating back upstream as whitebait in spring.
Banded kōkopu (Galaxias fasciatus)
Banded kōkopu have pale vertical stripes across their sides. Also called Māori or native trout, they dwell in pools with overhanging banks, logs and boulders.
Like other galaxiids, banded kōkopu have sensors on their heads to detect when and where something hits the water, enabling them to feed on insects that fall from overhanging plants.
They are good climbers and can be found up to 550 m above sea level. Most grow to around 200 mm long, but they can reach 260 mm. Banded kōkopu need stream-side plants to survive.
Giant kōkopu (Galaxias argenteus)
Giant kōkopu are the largest of all the galaxiids, not only in New Zealand, but around the world. Although individuals are usually 300–400 mm long, one specimen has been found weighing 2.8 kg and measuring 580 mm long.
Not the most adept of climbers, giant kōkopu are generally found close to the sea. They inhabit wetlands, lakes and forest streams, and rely on good bush surrounds. Giant kōkopu are skulking predators, lurking under cover and making speedy dashes to nab their prey.
They are slow-growing and can live for more than 20 years. Like the banded kōkopu, giant kōkopu are also called native or Māori trout.
Inanga (Galaxias maculatus)
Inanga are found in a wide variety of habitats, from tiny creeks, to coastal rivers, lowland streams, lakes and wetlands. They are the odd-balls amongst the whitebait species, having adults that swim together in shoals.
Inanga are small and short-lived, with most only surviving for 1 year and reaching around 100 mm in length—although the longest on record is 190 mm.
Because they are poor climbers, inanga are usually found near the coast. Their silvery belly and somewhat forked tail make them easy to distinguish. Found in places as far flung as Chile, Australia and Argentina, inanga are the most widely distributed native freshwater fish in the world. They are New Zealand’s most commonly caught species.
More on inanga.
Kōaro (Galaxias brevipinnis)
Kōaro are accomplished climbers, being able to negotiate near-vertical waterfalls using specially formed broad fins that have a grippy texture underneath.
Living for 15 years or more, kōaro travel as far as 400 km inland, and climb as high as 1300 m.
These solitary fish are often found in fast-flowing, cool, tussock or forest streams. They commonly grow to about 160–180 mm, but can reach 290 mm. In bright light, their skin shines with iridescence.
Shortjaw kōkopu (Galaxias postvectis)
Shortjaw kōkopu are rare, secretive and seldom seen. As the name suggests, they have an undercut jaw, which is probably designed to scrape aquatic insects from rocks.
Shortjaw kōkopu usually grow to between 150 and 200 mm, but can reach 370 mm.
Mostly found at low to moderate elevations, they inhabit bouldery forest streams. They can only survive in certain types of habitat, many of which have been degraded by forest clearance, which has probably contributed to their rarity. Shortjaw kōkopu are unique to New Zealand.