Unique Feeding of Garden Eels Has Been Revealed by Scientists

The epitome of the homebody is the garden eel. These eels anchor themselves into burrows on the sandy bottom and almost never leave them, as opposed to swimming freely in the water.

Their colonies, which are normally located on the periphery of tropical coral reefs, can include thousands of eels.

As the eels bob and wave, they give the impression of a garden of seagrass from a distance.

Their heads, complete with pouting mouths and adorable cartoon eyes, face away from the current as they pounce on zooplankton that is drifting by.

Garden eels' eating behavior

(Photo : Tomoko Saeki/Unsplash)

Scientists currently know very little about these unusual organisms and how their behavior, such as their feeding habits, varies with environmental factors, as per Sciencedaily.

The majority of oceanic research has concentrated on the more typical eating habits of free-swimming fish, and garden eels' timidity, which causes them to hide when predators approach, making research even more difficult.

Garden eels' eating habits have been studied by marine scientists at the Okinawa Institute of Science and Technology Graduate University (OIST).

Their research, which was published in the Journal of Experimental Biology, showed how garden eels, unlike much free-swimming fish, can eat in a larger range of flow speeds by using their burrows and altering their posture and movement in reaction to strong currents.

Kota Ishikawa, the first author and a Ph.D. student at OIST's Marine Biophysics Unit, explained that free-swimming fish can take refuge from currents by hiding in cracks and crevices in the reef.

However, because garden eels are confined to a more exposed location and have to rely only on their burrows for protection, they have had to evolve special defense mechanisms to deal with strong currents.

The researchers mimicked real-world circumstances by creating a flume with a sandy bottom specifically for the lab.

Each portable burrow, which contained a single spotted garden eel of the Heteroconger hassi species that is frequently seen on Okinawa, could be placed within the flume.

A deep learning computer was trained to detect and track the eye and topmost black patch on their body using the video that the cameras had recorded.

The researchers then used this monitored data to digitally rebuild and examine each eel's 3D movement and posture.

The 3D tracking revealed that when the current grew, the garden eels moved deeper into their tunnels and concentrated their attacks on nearby zooplankton.

To determine how many zooplankton the eel had managed to collect and consume, the researchers counted the leftover ones after each experiment was complete.

They discovered that the eels continued to feed quickly even after making a gradual retreat into burrows when the current's velocity rose to 0.2 m/s.

Ishikawa said that even though quicker currents restricted their feeding area, more zooplankton floated by in the allotted period, countering the behavior shift.

The eels had a better chance of catching the zooplankton due to their closer striking distance.

In addition, the eels assumed a curved stance at greater flows as opposed to a straighter posture at lesser flows.

This allowed the eels to conserve energy by lowering the portion of their body that was exposed to the river and reducing drag on their body by about 57%.

Also Read: The Fascinating Life of Eels, Which Breed Only During Their Last Year of Life

What do eels eat?

Eels consume mollusks, crabs, and fish.

Being carnivorous predators, they consume a wide variety of foods, including practically every marine animal that is smaller than themselves, as per a-z animals.

Eels are excellent hunters, but they are also cautious enough to stay away from things that may hurt them.

They consume a broad range of things, although their diets alter slightly depending on whether they are in freshwater or saltwater.

Eels can pursue a wider variety of marine creatures in saltwater than they do in freshwater, with access to more insects in particular.

Elvers, or baby eels, spend their first few weeks of life eating a range of nutrients that depend on where they dwell.

They mostly eat insects and little fish in freshwater.

The lack of access to insects causes them to be relatively herbivorous at sea, grazing on plankton until they are big enough to eat an adult diet.

Eels eat a variety of meals and are versatile predators that may survive anywhere. Additionally, given their environment, they often consume different quantities of food.

For instance, pet freshwater eels are often fed once daily, but saltwater eels only receive food approximately three to four times each week.

However, the latter eel has a more varied and nourishing diet.