Short-finned eel facts for kids
Quick facts for kids Short-finned eel |
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The short-finned eel (Anguilla australis) is a type of eel found in the waters of Australia, New Zealand, and many islands in the South Pacific. It's one of 15 different kinds of eels in the Anguillidae family. You can find them in lakes, dams, and rivers near the coast. These eels are also known as the shortfin eel.
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About the Short-finned Eel
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Short-finned eels have long, snake-like bodies. Their bodies are mostly round, and their heads are small. Their jaws reach back to below their eyes. The fin on their back (called the dorsal fin) and the fin on their belly (called the anal fin) are about the same length.
Their color can change a lot. They are often a deep olive-green. But some can be lighter, like golden or even yellowish. They don't have any special markings. Their underside is usually pale, often silvery. Their fins are greenish.
When fully grown, these eels can reach about 90 centimeters (about 3 feet) long. Female eels can grow up to 1.1 meters (about 3.6 feet) and weigh 3 kilograms (about 6.6 pounds). They usually live for 15 to 30 years. Male eels tend to grow slower and stay smaller. The sex of an eel is decided as it grows, usually when it reaches a certain size.
Where Short-finned Eels Live
Short-finned eels are common in the lowlands of New Zealand. This includes Chatham Island and Stewart Island. However, they usually don't travel as far inland as the long-finned eels.
In Australia, you can find them along the coast. They live from Mount Gambier in South Australia, through Victoria and Tasmania. They also live along the eastern coast up to the Richmond River in New South Wales. They cannot cross the Great Dividing Range, which is a large mountain range. This means they don't live in the many waterways that flow inland in eastern Australia.
The tiny baby eels, called larvae, float on ocean currents. They eventually reach coastal waters. There, they change into elvers. Elvers are small, see-through eels. From the coast, they swim upstream into rivers. They can even leave the water and travel short distances over wet ground. They are good at this because they can breathe half the oxygen they need through their skin.
Eventually, they settle in a lake, swamp, dam, or river. They usually stay in an area about 400 meters (about 1,300 feet) long. They live there until they are ready to reproduce. Males mature around 14 years old, and females between 18 and 24 years old.
What Short-finned Eels Eat
Short-finned eels are carnivores, meaning they eat meat. Their diet includes crustaceans like crabs, other fish, frogs, and even small birds.
Life Cycle and Reproduction
Like other eels in their family, short-finned eels are catadromous. This means they live in freshwater but travel to the sea to reproduce. When they are mature, they stop eating. Then they migrate downstream to the ocean. They can travel up to three or four thousand kilometers (about 1,800 to 2,500 miles). They go to a special place in the Coral Sea near New Caledonia to lay their eggs.
The baby eels, called larvae, are born in the sea. They are very small and transparent. When they return to coastal waters, they are called 'glass eels' because they are clear. Eels in tropical areas can reproduce all year. But temperate eels, like the short-finned eel, have a strong breeding season. Some eels might even stay in the ocean or estuaries and rarely enter freshwater.
The exact details of their reproduction in the ocean are still a bit of a mystery. Scientists know a lot about their lives in freshwater. But less is known about their time in the sea. Warmer water temperatures seem to help tropical eels grow faster.
Short-finned eels are very tough. They can handle warm water and low oxygen levels. They can also go long periods without food. If the water gets too cold (below 10°C), they can bury themselves in mud or sand. They then enter a sleepy state to save energy. They are one of the few Australian freshwater fish that have done well even with many new fish species introduced from Europe and America.
Eels and Fishing
People have been catching short-finned eels for a long time. The chart shows how many tonnes of short-finned eels were caught globally between 1950 and 2009.
Eel Farming
Eel farming was tried in New Zealand in the 1970s. It didn't work very well back then. But new technology has made farming eels a better idea now. It's more efficient to produce them. The NIWA (National Institute of Water and Atmospheric Research) is working on new ways to raise eels in freshwater. They are also looking into farming them in saltwater.
Decline of Wild Eels
One big reason eel farming has become more popular is that there aren't enough wild eels to meet demand. The number of European and Japanese glass eels being caught has gone down. This makes short-finned eels more valuable. The pressure on wild eels means fewer young eels are growing up. This affects both the fishing industry and the environment.
Eel farms rely on catching wild glass eels to raise them. They cannot raise eels from eggs in a farm setting. Because wild eel numbers are dropping, there is a need to develop better ways to farm eels.
History of Eel Farming
The Gunditjmara people of western Victoria, Australia, developed large systems to farm short-finned eels. These systems were built at least 7,000 years ago. They used wetlands created by lava flows from the Budj Bim volcano. The Gunditjmara people called the eel kooyang. Today, these areas are protected as part of the Budj Bim heritage sites.
Current Eel Industry
Short-finned eels are very tasty, so people around the world want to eat them. Japan is the biggest market for eels. Other parts of Asia and Europe also buy them. Raising animals for food, called aquaculture, is the fastest-growing food sector globally.
Worldwide, about 242,000 tonnes of eels are produced from aquaculture each year. This is worth about 1 billion US dollars. China's eel farming has grown a lot in the last 10 years. It now produces 75% of all farmed eels in the world. This industry mostly serves the Japanese market.
Scientists have been studying how to breed Japanese eels in captivity since the 1960s. It is hard to raise eels completely on farms. The main challenges are getting them to reproduce fully and raising the tiny larvae. Scientists often use special injections to help female eels lay eggs.
Growing the Eel Industry
To make eel farming grow, we need a steady supply of young eels. We also need to understand more about the eels' biology. This includes knowing when they reproduce in freshwater. It also means making sure we don't catch too many eels from the wild.
New Zealand is in a good position. Even though many short-finned eels are caught there, their numbers don't seem to be dropping much. So, New Zealand could help increase the world's supply of short-finned eels. This would take pressure off eel populations in other countries like China and Japan.
Most eel farms use freshwater. But one saltwater eel farm in the United Kingdom used warm seawater. It grew eels to market size in 18–24 months. It closed for money reasons.
Water temperature affects how fish grow. Eels can live in many temperatures. But the best temperature for farmed eels is between 22°C and 28°C. This is where they grow the most. Recent studies show that 26.5°C is best for short-finned eels. They also grow best when the water is a bit salty, around 17.5% salinity.
Making Eel Farming Sustainable
A big challenge for eel farming is controlling how they reproduce and develop. In farms, there are often more male eels than female eels. Males are smaller than females. Many fisheries try to focus on raising females. However, adding hormones to favor females is not allowed everywhere.
Short-finned Eels as Food
Short-finned eels are considered excellent food. They have been an important food source for a long time. Eating short-finned eels is a tradition in many Pacific nations. This includes Japan, Australia, and New Zealand.
Before Europeans arrived, two Aboriginal Australian groups, the Gunditjmara and the Djab wurrung, farmed eels on a large scale. They would smoke the eels and trade them with other communities for goods.
For the Māori people of New Zealand, eels were a very important food. They had advanced ways of fishing for freshwater eels before Europeans came. Māori people knew a lot about eels and used many different ways to catch them. Today, people still catch and eat them for fun. New Zealand also has a commercial eel fishing industry. Māori people are now worried that commercial fishing might make it harder for them to catch eels for their traditional ceremonies.
Froese, Rainer and Pauly, Daniel, eds. (2005). "Anguilla australis" in FishBase. 10 2005 version.
See also
In Spanish: Anguilla australis para niños
