TREASURES / TAONGA

Aotea’s Freshwater Fish

whitebait migratory galaxiids

Whitebait are the juveniles of six species of fish. Five of these are migratory galaxiids: inanga, banded kōkopu, giant kōkopu, kōaro and shortjaw kōkopu. The sixth species is common smelt. Banded Kokopu and Inanga are common on Aotea, Great Barrier Island and Giant Kokopu have been reported.

Banded kōkopu

Galaxias fasciatus
Special fact! Banded Kokopu are also called Māori or native trout. They are generally the smallest of the five species when they are whitebait and have an overall golden colour. The juveniles are very good climbers and will often escape from buckets by clinging to and wriggling up the sides. 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.
Features: Banded kōkopu have pale vertical stripes across their sides. These bands begin to develop quite early, but similar bands also appear on juvenile giant kokopu, and it is easy to confuse young fish of these species.
Feeding: Terrestrial and aquatic insects
Threats: Habitat degradation, barriers to migration, over fishing
Status: Not Threatened
Where: They occur only in New Zealand. Adult banded kokopu usually live in the pools of very small tributaries where there is virtually a complete overhead canopy of vegetation. This vegetation does not have to be native bush, however, and banded kokopu happily live in urban streams and streams under exotic pine plantations so long as overhead shade is present. They only occur in pools where there is instream cover such as an undercut bank, large rocks or wood debris. They depend on terrestrial insects for a large proportion of their diet and can detect the small ripples made by moths and flies that become stuck on the water surface of the pool.

Photo credit: Taryn Wilks

Inanga

Galaxias maculatus
Special facts: Inanga (Galaxias maculatus) are the most common native fish species caught as whitebait. They are the only migratory galaxiid species where the adults swim 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.
Lifecycle: Inanga have an unusual lifecycle. They begin life as eggs laid in vegetation beside streams in late summer and autumn. When the eggs hatch, they are carried downstream as larvae and spend the next six months at sea. In the spring they migrate upstream as whitebait and grow into adult fish
Features: Their silvery belly and somewhat forked tail make them easy to distinguish. You can pick out inanga from the mix of whitebait in a catch by their tiny, black mouths. They also have spots along their bodies and in front of the dorsal fin on their backs. Inanga have slim bodies and are often longer than other species in whitebait.
Feeding: Insects
Threats: Habitat degradation, barriers to migration, over fishing
At risk: Declining
Where: Inanga are poor climbers and live in lowland freshwater habitats like coastal creeks and streams, rivers, lagoons, lakes, estuaries and wetlands. Unlike other migratory galaxiids, they don’t travel long distances inland as they have difficulty swimming through swift-flowing rapids and cannot climb past waterfalls. Adult inanga often swim in shoals and can be seen roving around during the daytime feeding on tiny insects. The adults of other migratory galaxiids tend to live a more solitary and nocturnal life. Although inanga are native to New Zealand and some of its offshore islands, they are also found in other Southern Hemisphere countries including Australia, Chile, Argentina and the Falkland Islands.

Photo credit: DOC & Taryn Wilks


giant kōkopu

Galaxias argenteus
Special Facts! Giant kōkopu are the largest of all the galaxiids, not only in New Zealand, but around the world. 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. Although individuals are usually 300–400 mm long, one specimen has been found weighing 2.8 kg and measuring 580 mm long.
Features: The profusion of golden spots and other shapes on the bodies of larger fish are very distinctive, although small specimens may be difficult to distinguish from banded kokopu. The giant kokopu was the first Galaxiidae to be discovered, and it was its colour pattern that led to the generic name Galaxias, referring to the profusion of stars in the galaxy.
Feeding: Giant kōkopu are skulking predators, lurking under cover and making speedy dashes to nab their prey.
Threats: Habitat degradation, barriers to migration, over fishing
Status: Declining
Where: 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.

Photo credit Auckland Council

EELS / TUNA

There are two main species of freshwater eel found in New Zealand, the longfin eel (Anguilla dieffenbachii) and the shortfin eel (Anguilla australis). There is a third species, the spotted eel (Anguilla reinhardtii) is an occasional visitor from Australia. 

 

Eels migrate up streams as elvers to find suitable adult habitat.  After many years (15-30 years for shortfins, 25 years for longfins, and sometimes up to 80 years) they migrate to the Pacific Ocean to breed and die. Eels are secretive, mainly nocturnal and prefer habitats with plenty of cover. 

Longfin Eel

Special Facts! When eels begin life, they are a tiny one millimetre in length. During their life, they can grow up to two metres long. The biggest eels are usually old females that have been slow to reach sexual maturity and, for reasons that are not yet understood, have not migrated to sea to breed. Eels hunt by smell rather than sight. Longfin eels have a well-developed sense of smell. They have tube nostrils that protrude from the front of their head, above their upper lip.
Lifecycle: Longfin eels breed only once, at the end of their life. When they are ready to breed, they leave New Zealand and swim all the way to the sub-tropical Pacific Ocean to spawn, probably in very deep ocean trenches. When they reach their destination, the females lay millions of eggs that are fertilised by the male. The larvae are called leptocephalus and look nothing like an eel – they are transparent, flat, and leaf-shaped. The larvae reach New Zealand by drifting on ocean currents. Before entering fresh water, the leptocephalus change into a more familiar eel shape, although they remain transparent for up to a week after leaving the sea. These tiny “glass” eels enter fresh water between July and November each year, often in very large numbers.
Features: Big loose wrinkles on the skin when bent. The longfin eel is so named because its top (dorsal) fin is longer than its bottom fin. In colour, longfins are usually dark brown to grey black. Very occasionally, longfin eels found in the wild are partially or even wholly bright yellow in colour.
Feeding: Eels eat “live” food. Small longfin eels living amongst the river gravels will feed on insect larvae, worms and water snails. When they get bigger, they begin to feed on fish. They will also eat fresh-water crayfish and even small birds like ducklings.
Threats: Habitat loss, degradation, pollution and over fishing
Status: At Risk – declining
Where: Longfin eels can be found throughout New Zealand. They live mainly in rivers and inland lakes but can be found in almost all types of waters, usually well inland from the coast. They are legendary climbers and have made their way well inland in most river systems, even those with natural barriers. Elvers (young eels) swimming up river will climb waterfalls and even dams by leaving the water and wriggling over damp areas. It is not unheard of for an eel to climb a waterfall of up to 20 metres.

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Photo credit: DOC

Bullies (Eleotridae)

Bullies have rounded tails, two dorsal fins, a blunt head, and are quite stocky. They can sometimes be recognized by their habit of sitting on the substrate looking almost as if they were standing up on their forward fins. They have a darting method of swimming and usually remain on or close to the substrate. Members of the bully family occupy marine and fresh waters in the tropical Pacific and southeast Asia. There is just one freshwater genera in New Zealand, Gobiomorphus.

Common bully

Gobiomorphus cotidianus
Special fact! Even though they are well camouflaged against sand and rocks, common bully are often seen darting in the shallows during the day. Eggs are laid on the undersides of hard substrates (wood, rock) in lakes and rivers. The male guards the nest and when the eggs hatch, the larvae go to sea to return to freshwater after a few months. However, some populations become landlocked and complete their life cycle without the sea phase.
Features: Rounded tails, two dorsal fins, a blunt head, and are quite stocky
Feeding: Insects
Threats: Habitat degradation, barriers to migration
Status: Not Threatened
Where: Sea-going populations occur in river and streams near the coast, and land-locked populations have become established in many of our lakes where they are an important prey species for trout and eels. In rivers, they mainly inhabit still or slow-flowing waters and thus are probably one of the most likely bullies to be seen. In lakes, the larvae are planktonic and feed on zooplankton. Eggs are laid on the undersides of hard substrates (wood, rock) in both lakes and rivers, and the egg patches are defended by a male.

Photo credit: DOC

giant bully

Gobiomorphus gobioides
Special fact! This dark-coloured fish prefers lowland waterways especially estuaries and is almost always found beneath cover, only to emerge at night to feed. It can grow over 15 cm long. It is presumed that giant bullies have a marine phase in their life cycle, but this is not known for sure. It is virtually impossible to distinguish the giant bully from the common bully unless you count the number of spines in the first dorsal fin. In giant bullies there are always six spines and in common bully there are usually seven.
Lifecycle: The life cycle of giant bullies is somewhat of a mystery. The larvae are thought to have a marine phase, but no juvenile giant bullies have ever been positively identified.
Features: Dark-coloured fish. As its name implies, the giant bully is the largest member of the Eleotridae family in New Zealand. Specimens of over 250 mm in length have been reported, although fish in the 120-150 mm range are more common.
Feeding:
Threats: Habitat degradation, barriers to migration
Status: Naturally Uncommon
Where: Lowland waterways, especially estuaries. They prefer, slow-flowing coastal habitats and are never found more than a few kilometres inland.

Photo credit: M. Dowall and Science Learning Hub

redfin bully

Gobiomorphus huttoni
Special fact! The bright red fins of an adult male redfin have to make this one of New Zealand’s most attractive freshwater fish. The redfin bully is strictly diadromous (spend part of their life cycle in freshwater and marine) and does not establish in land-locked waterways like lakes. They tend to live near the coast, even though they are very good climbers (populations above 5-metre high waterfalls have been recorded).
Lifecycle: Spawning takes place in freshwater, where the male guards the nest before the larvae get washed out to sea. The juveniles enter freshwater in the spring and reach maturity about 2 years later.
Features: Male redfin bullies are our most colourful native fish, with bright orange-red fins. Although only males get this distinct colouration, the diagonal stripes on the cheeks make the redfin bully easy to identify.
Feeding: Insects (primary food is mayfly, caddisfly and chironomid larvae)
Threats: Habitat degradation, barriers to migration
Status: Not Threatened
Where: Redfin bullies occur mainly in the runs and riffles of small bouldery streams. Because of their dependence on this habitat, they are more sensitive to the effects of siltation in streams than other fish species.

Photo Credit: S.C.Moore & Taryn Wilks

Information source www.doc.govt.nz