Garden Eel

Garden Eel – The first laboratory study of garden eels shows how these shy creatures use their burrows and change their movements and postures when feeding in strong currents.

Garden eels are the best pets. Instead of swimming freely in the ocean, these eels anchor themselves in burrows on the sandy bottom and hardly ever leave. Their colonies, usually on the edge of tropical coral reefs, can consist of thousands of eels, which from a distance look like a sea grass garden. Their heads, complete with puffy mouths and cute cartoon eyes, work against the current as they attack tiny animals called zooplankton.

Garden Eel

Garden eels anchor their lower bodies in caves and hold their heads against the current while they hunt for zooplankton. The species depicted is the spotted garden eel, Heteroconger hassi.

Study Reveals The Secret Feeding Strategies Of Garden Eels •

Currently, scientists know relatively little about these unique creatures and how their behavior, such as how they eat, changes depending on environmental conditions. Most marine studies focus on the more common feeding strategies of free-swimming fish, and the shyness of the gardener, which hides when predators (or divers) pass by, makes them even more difficult to study.

Now, for the first time, marine scientists from the Okinawa Institute of Science and Technology () looked at the feeding behavior of garden eels under experimental laboratory conditions. Their findings, published in the Journal of Experimental Biology, reveal how garden eels use their burrows in response to strong currents, changing their movements and postures, allowing them to feed in a wider range of current speeds than many free-ranging fish. swimming fish.

“Free-swimming fish can hide from currents by hiding in cracks and crevices in the reef,” said Kota Ishikawa, first author and graduate student in the Division of Marine Biophysics. “But garden eels are stuck in a more open area, with only their nests, so they’ve had to develop their own unique strategies to deal with strong currents.”

In the laboratory, researchers recreated typical conditions by creating a channel with a sandy bottom. Inside the hole was a place to place a portable nest, each nest containing a spotted garden eel.

Splendid Garden Eel

In the experiments, the researchers added zooplankton to the water and used cameras, two from the side and one from above, to capture the movement of garden fish feeding at four different flow rates: 0.1, 0.15, 0.2 and 0.25 m/s. .

The images captured by the cameras were then used to train a deep learning program to recognize and track the eye and the top black spot on the body. From this tracked data, the researchers digitally reconstructed and analyzed the 3D movement and posture of each eel.

As the flow increased, 3D tracking showed garden eels retreating further into the burrows and directing their attacks at zooplankton passing nearby.

After each trial, the researchers counted the remaining zooplankton to determine how much the eel was able to catch and eat. They found that as the current speed increased to 0.2 m/s, the eels did not stop feeding rapidly as they slowly retreated to the wells. This is because, Ishikawa explained, although it limits the feeding area, faster currents compensate for the change in behavior, meaning more zooplankton move past in a given time. A shorter stroke distance also meant that snakes were more likely to catch zooplankton.

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At higher currents, the eel also assumed a curved posture, as opposed to the straighter posture seen in slower currents. This, along with reducing the amount of body exposed to current, allowed the eels to reduce the amount of body friction by approximately 57%, saving energy.

The researchers created digital 3D constructions to analyze how garden eels change their attitude and distance from the nest.

But some currents are simply too strong even for garden hoses. After the flow rate reached 0.25 m/s, the garden eels retreated completely into their burrows and did not forage at all.

Overall, the researchers found that the garden eel’s feeding speed peaked at 0.2 m/s. Free-swimming, plankton-eating fish typically have peak feeding rates of approx. 0.15 m/s, indicating that the gardener is adapted to feed over a wider range of current velocities than free-swimming reef fish.

Spotted Garden Eel

“We can see that their unique strategy of pulling into holes and reducing stroke is paying off when fighting very strong currents,” Ishikawa said.

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Garden Eel Small

Research Update researchers were awarded a JST FOREST grant. Dr. Yosuke Yamada, Dr. Reina Komiya and Prof. Ryota Kabe were awarded a place in the FOREST (Fusion Oriented REsearch for Disruptive Science and Technology) program.

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It occurs in sandy areas exposed to sea grass at depths between 18 and 75 m, but is usually observed at an average depth of 30 m.

The beautiful gard eel lives either alone or in groups of three to a thousand in a tube buried in the sand.

Spotted Garden Eel Heteroconger Hassi. Stock Photo

Usually only the head and upper body protrude from the sand and will retreat in exhaustion if large fish or divers approach. They feed on crawling plankton.

During the mating season, male and female eels will move their nests to increase their proximity to each other. Males will often show protective behavior in courtship and may bite rival eels. After a male has won a display, the male and female needle will extend out of the nest with their bodies wrapped around each other.

Spldid gard eel are pelagic spawners, which means that the female eel will release fertilized eggs. Once the eggs hatch, the larvae continue to swim until they reach a certain size. When they reach this size limit, the baby eels will dig sand pits. When diving in tropical waters, you may come across what appears to be seagrass beds moving gently with the current. But look closer – you are actually swimming among a colony of spotted garden eels (

), thin and straw-like fish that are often mistaken for plants, they spend most of their lives submerged in the ocean floor. Spotted garden eels, one of many species in the subfamily Heterocongrinae, live in areas with strong currents, where they swim together in large groups and feed on zooplankton; A colony can have hundreds or thousands of eels.

Cortez Garden Eel, Heteroconger Digueti, La Paz, Baja California Sur, Mexico Stock Photo

Garden fish may be small compared to other species (only half an inch in diameter), but what they lack in size is muscle.

It uses its hard, muscular tail to burrow through the sandy bottom, then secretes a slimy mucus that acts as cement to prevent the nest from collapsing. When disturbed, the garden eel pulls its tail first into a hole. predators. Shy and cautious, they will slowly pop their heads out of the nest after the danger has passed.

The spotted garden eel is widespread from the Indo-Pacific and northwest Australia to the Red Sea and East Africa and is found in waters up to 150 feet deep. Colonies are usually found on sand flats and slopes bordering coral reefs, sometimes living among sea grasses for added camouflage.

Garden eels will generally leave their original nests during the spawning season to be close to their mates. If two males get too close, they may fight over territory and nearby females. During mating, garden eels wrap their upper halves together, and their tails remain in their separate nests. During a mating, two eels can stay like this for hours. Garden eels are pelagic spawners; they release fertilized eggs into open water, which then float near the surface with the current. When the eggs hatch, the small nymphs are free-swimming until they are large enough to form their own nests.

Zebra / Banded Garden Eel (heteroconger Polyzona)

A garden eel’s best defense is a quick retreat to the nest, but some predators, including eels and minnows, have developed creative ways to get there.

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