Common river galaxias facts for kids
Quick facts for kids Common river galaxias |
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The common river galaxias or Canterbury galaxias (Galaxias vulgaris) is a small, freshwater fish. It belongs to the Galaxias family and is found only in the Canterbury area of New Zealand.
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What Does It Look Like?
The common river galaxias is a small fish, usually growing to about 10 to 11.5 centimeters (4 to 4.5 inches) long. It has a big mouth with a lower jaw that sticks out a bit. Its nose is rounded, and its nostrils are a bit pinched.
Its fins are thick and strong. The fins near its head (pectoral fins) point downwards. The part of its body leading to its tail (caudal peduncle) is long and thin.
This fish is an amazing master of disguise! Its skin is speckled brown, grey, or olive green. This helps it blend in perfectly with the gravel at the bottom of rivers. It also has black stripes or blotches along its back. This special coloring is so good that it can safely swim out from under rocks into the open river.
It can sometimes be confused with another fish called the koaro. But you can tell the common river galaxias apart because its eyes are bigger and point more towards each other. It also has less dense spots and is a bit wider and larger than some other similar fish.
Where Does It Live?
You can find the common river galaxias in rivers and streams across the Canterbury area of New Zealand's South Island. However, you won't find it in Banks Peninsula or eastern Otago. These fish live in shallow waters, from low lands up to high mountain areas.
Sadly, you won't find them in many of the main river systems anymore. This is because of bigger, introduced fish like rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta), which eat them.
Favorite Places to Live
Common river galaxias love fast-flowing parts of streams where the water has lots of oxygen. They prefer areas surrounded by open tussock grasslands. During the day, they hide under and between rocks. At night, they come out into the open water to find food. They are usually shy and hunt alone in the dark.
Because of the trout, these galaxias are often pushed out of the main rivers. But you can still find them in smaller side streams and tributaries (smaller rivers that flow into a larger one).
These fish don't travel to the ocean. They spend their whole lives in the same river system where they were born. This means different groups of galaxias in different rivers are often separated. They might only meet other groups during big floods when water levels are very high.
Life Cycle
Unlike some other fish in its family, the common river galaxias stays in freshwater its whole life. It doesn't travel to the sea.
They lay their eggs from August to September. The female fish lays hundreds to thousands of tiny eggs under large rocks in the stream. The number of eggs depends on how good the environment is. The male fish then fertilizes the eggs and guards them for a short time. The male digs out a "nest," and often, several females will lay their eggs in the same nest.
Compared to other freshwater fish that don't travel, the common river galaxias lays many small eggs. This helps them spread quickly and re-populate areas. However, because of predators and other challenges, many young fish don't survive, and adults often die after laying eggs.
The tiny baby fish, called larvae, hatch from the eggs after about 3 to 4 weeks. They are only about 7 to 8 millimeters long. They swim together in groups in the slow-moving edges of the stream. They stay in these groups until they grow to about 3.5 centimeters (1.4 inches). At this size, they have developed their special camouflage and can leave the group to live on their own.
Young galaxias become old enough to have their own babies in early autumn. Their size, not the time of year, is the main thing that tells them when they are ready to reproduce. They usually need to be about 5.9 centimeters (2.3 inches) long.
What Do They Eat?
The common river galaxias mainly eats the young forms (nymphs and larvae) of invertebrates, which are creatures without backbones. They mostly live near the bottom of the river.
They are active at night. During the day, they hide in the gravel and under rocks. After sunset, they come out and swim in the water, catching food that floats by. Later in the night, they switch to finding food on the riverbed. They swim facing the current and grab food as it washes towards them.
Their diet includes small stream insects like stoneflies and mayflies. When they are catching food floating in the water, they prefer bigger prey. Studies of their stomach contents have shown they eat lots of caddisfly larvae, dobsonfly larvae, mayfly larvae, and different types of aquatic and land insects.
Who Are Their Enemies?
The main enemies of the common river galaxias are the introduced rainbow trout and brown trout. These trout can seriously harm galaxias populations.
In areas where there are no trout (often in higher altitude streams that are geographically isolated), the galaxias populations are much more stable. Trout eat galaxias at all stages of their lives, so there's no size at which a galaxias is completely safe from trout. However, young galaxias are especially easy targets for trout of all sizes.
Protecting the Common River Galaxias
In 2014, New Zealand's Department of Conservation listed the common river galaxias as "At Risk: Declining." This means their numbers are going down. However, the IUCN also rated the species as "Least Concern," noting that their decline is slow.
Many areas where the common river galaxias live are managed by New Zealand's Department of Conservation, which helps protect them. But the invasive trout are still a big threat.
Another danger to the common river galaxias is the loss of their habitat. This happens when land is changed for farming, especially with more irrigation. The IUCN has noted that there's a higher risk of habitat loss in the high country areas after land ownership changes. Much of this land, which includes galaxias habitat, can now be used for farming, putting the fish's home at risk. Even with these threats, the common river galaxias is currently classified as "Not Threatened."
