Inanga

Size and appearance

Inanga are the smallest migratory galaxiid, reaching around 100 mm in length. The longest inanga on record is 190 mm. They have speckled olive-coloured backs and no scales. Their silvery bellies and slightly forked tails make them easy to distinguish from other native fish.

Inanga are also the only migratory galaxiid species where the adults swim in shoals. Inanga are short-lived, with most only surviving for 1 year.

Juvenile inanga have distinctive black mouths.

Where inanga live

Inanga live in coastal creeks and streams, rivers, lagoons, lakes, estuaries and wetlands. Unlike New Zealand’s 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 during the daytime feeding on tiny insects. The adults of other migratory galaxiids tend to be more solitary and are generally seen at night.

Although inanga are native to New Zealand and some of its offshore islands. This species is the most widely distributed native freshwater fish in the world. Besides New Zealand, inanga are found in Australia, Chile, Argentina and the Falkland Islands.

Inanga lifecycle

Eggs are laid on land

A few days before a full and new moon from February to May, inanga migrate downstream to the place where fresh water meets sea water coming upstream. They congregate here, waiting for a very high, spring tide.

As the tide rises, shoals of inanga work their way along the bank, pushing into the flooded vegetation at the very edge of the water. They choose the base of tall, dense vegetation to lay their eggs. Each female can release up to 13,000 eggs, which are 1.2 mm in diameter.

After the tide goes down, the eggs are stranded until the next spring tide. Streamside plants protect them from dehydration, extremes of temperature and damaging UV radiation, but natural predators like herons and eels seek them out for food. The eggs can also be damaged by bacterial and fungal infections, drought and flood.

Larvae move to the sea

Eggs develop for 2–4 weeks, depending on the temperature. When the water from the next spring tide reaches the fully developed eggs, they are stimulated to hatch and are carried downstream to the sea. The tiny larvae grow quickly, feeding on plankton in coastal waters for 6 months.

Juveniles return

By spring the juvenile fish have grown to about 55 mm in length and start to migrate into rivers and streams. Juvenile inanga are the most common species of native fish caught as whitebait as they move into rivers and stream mouths.
They spend the summer in backwaters and slow-flowing sections of rivers and streams, growing into adult fish.

Life as an adult

Inanga feed on tiny insects in the open water. They grow to 80–110 mm in length and have a bright silver abdomen and a speckled olive-coloured back. Inanga have no scales and look transparent.

By late summer most inanga are mature and ready to spawn. Many fish die after spawning but some live for another year. Spawning takes so much energy that the fish are left in poor condition and are at greater risk from disease and predators.

A diagram showing how adult fish create eggs that then turn to larvae and then whitebait before becoming adult fish.

Inanga lifecycle
Image: DOC | DOC Crown Copyright