Eels are one of the most odd-looking creatures in the ocean. Despite their similarities in appearance, they are not related to snakes. They are fish with long dorsal fins. They live in freshwater, reefs, and even the deep sea. From their interesting migration to their long lifespans, here are 15 fun facts about eels.
Eels from the class Actinopterygii belong to the Anguilliformes3, which boast the largest and most diverse group of bony fishes, comprising about 96% of all fish species. Known for their distinctive elongated, wormlike bodies, eels lack pelvic fins and, in most cases, pectoral fins. Instead, they possess a continuous dorsal, anal, and caudal fin that runs around their tail tip.
With over 800 known eel species, eels stand out as an incredibly diverse group of fish. Their classification further emphasizes this diversity into eight suborders, 19 eel families, and 111 genera.
Various eel families have varied colorations. Tropical reef species often showcase vibrant and eye-catching colors like yellow, green, brown, and even blue or purple. Deep-sea species are commonly black, brown, or drab gray, allowing them to blend in with the dimly lit surroundings.
Additionally, some exhibit bioluminescent features. On the other hand, freshwater eels have brown, green, or black colors, which provide effective camouflage in the murky and vegetated environments of rivers, lakes, and ponds.
Various eel species inhabit different habitats, showcasing their remarkable adaptability and ecological diversity. In freshwater habitats, European Eel (Anguilla anguilla) and the American Eel (Anguilla rostrata) thrive in rivers, streams, and lakes across different continents. These eels spend most of their lives in freshwater systems and migrate into the Sargasso Sea for spawning.
Some species, like Japanese Eels (Anguilla japonica), native to Japan and East Asia, live in coastal and estuarine environments. Similarly, the New Zealand Longfin Eel (Anguilla dieffenbachii) is found in New Zealand's coastal and estuarine regions, showcasing a similar migratory behavior between freshwater and coastal waters. However, species like the Moray Eels remain on the ocean all their lives.
On the other hand, the Snipe Eel (Nemichthys scolopaceus) is a species adapted to the dark and cold conditions of the deep ocean. These eels live at significant depths, often beyond 1,000 meters.
The giant eels, like the Slender Giant Moray, can grow up to 13 feet long. These impressive predators dominate tropical waters with their power and size. The European Conger (Conger conger) is the heaviest species and can weigh as much as 240 pounds.
On the other hand, small eels, such as the One-jawed Eel (Monognathus Ahlstrom), can be as tiny as 5 centimeters. And have you ever heard of garden eels? These adorable creatures live partially buried in the sand, creating a mesmerizing sight that resembles a "garden" of eels.
Eels feed on small fish and invertebrates, such as crustaceans and mollusks. Some larger eel species may also consume amphibians, small reptiles, birds, or small mammals if available. Moray Eels can even eat octopuses.
Their jaws are uniquely built, allowing them to gulp down their prey in a single, swift motion. And despite their teeth being small, they are incredibly sharp and perfect for gripping onto their struggling meals.
These creatures are nocturnal hunters, preferring to move under the cover of night. They don't chase; instead, they wait, hidden among rocks or concealed in the sand, ready to strike when their prey least expects it. Their eyesight might not be the best, but their sense of smell more than makes up for it.
Next on our interesting eel facts list: Eels are not snakes, despite their similar appearance at first glance. While they may share some physical characteristics, they belong to different biological classifications. Eels are fish, explicitly belonging to the order Anguilliformes, while snakes are reptiles, belonging to Squamata.
Eels have gills and breathe through them, relying on aquatic environments to survive. In contrast, snakes have lungs and are adapted for terrestrial habitats, though some can also be found in marine environments. Also, eels have fins that aid their swimming, while snakes lack limbs or fins. The presence of scales and skin type also differ between the two groups, with eels having slimy, mucus-covered skin and snakes having dry scales.
These fantastic fish moves in an undulating pattern. Furthermore, they can swim backward and forward thanks to their continuous dorsal and anal fins that run along most of their body. Backward swimming serves multiple purposes for eels.
It helps them retreat from danger quickly and navigate through tight spaces like rocky crevices or dense vegetation to find shelter easily.
Generally, most eel species are long-lived and slow to reach sexual maturity. Some species may take several years to several decades before they become sexually mature. For example, European eels (Anguilla anguilla) typically take 5 to 20 years to reach sexual maturity, while American eels (Anguilla rostrata) may take 5 to 25 years or even longer.
Some species of eel, like the American and European eels, migrate for mating. They travel thousands of kilometers, which can take several months, to reach the Sargasso Sea, their marine nesting grounds. The exact triggers for this mass migration have yet to be fully understood. However, environmental cues, such as changes in water temperature and lunar cycles, are believed to play a role.
Interestingly, migratory eels only breed once. Adults ultimately die after reproducing.
The second phase of the eel's life cycle involves hatching the eggs into transparent, leaf-shaped larvae known as leptocephali. These larvae drift with the ocean currents for several months. Eventually, they reach coastal areas, where they metamorphose into glass eels, becoming more recognizable as juvenile eels or elvers1.
These glass eels then swim upstream and enter freshwater systems where they find their juvenile and adult habitats. During their freshwater phase, which can last for several years or even decades, depending on the eel species, they mature into yellow eels.
Finally, when the time is right, the yellow eels undergo another transformation, developing darker pigmentation and becoming silver eels. These silver eels then migrate back to the Sargasso Sea to complete the cycle and repeat the reproduction process.
The electric eel (Electrophorus electricus) is not a true eel but belongs to a different group of fish known as knife fishes, which are part of the order Gymnotiformes. While they share some similarities with true eels in appearance, they are biologically distinct.
Electric eels are known for their electrical abilities, and this ability is absent from true eels. They possess three specialized organs, the Sachs organ, the Main organ, and the Hunter's organ, which are modified muscle cells capable of generating electric discharges2.
Read more: Electric Eel Facts You Might Not Know.
While most eels are solitary during their juvenile and adult life, garden eels are captivating creatures known for their social behavior and the formation of vast colonies in specific tropical reef areas. Garden eels typically inhabit sandy or muddy substrates in shallow tropical waters, often in areas with moderate water flow.
What sets them apart from most eels is their unique way of living. Instead of hiding in crevices or rocks like many other eel species, garden eels partially bury themselves in the sandy or muddy seafloor, exposing only their upper bodies.
The Longfin Eel (Anguilla dieffenbachii), also known as the New Zealand Longfin Eel, is a fascinating species with an exceptionally long lifespan. Remarkably, these eels can live up to a century, making them one of the longest-lived freshwater eels in the world.
This impressive longevity results from their slow growth rate and the absence of significant predators in their native habitats, allowing them to reach old age relatively undisturbed.
Eel meat holds significant cultural and culinary importance in Japan, where it has been a delicacy for centuries. Unagi, the Japanese word for eel, is a beloved dish popular during summer.
One of the most famous Japanese eel dishes is "Unadon," which consists of grilled eel served on a bed of rice and drizzled with a sweet and savory soy-based sauce. The appreciation of eels in Japan is not just limited to their taste; it is also deeply rooted in cultural traditions.
The custom of eating eel during the summer season is believed to provide stamina and energy to endure the hot and humid weather. In particular, the midsummer day known as "Doyo no Ushi no Hi" (Day of the Ox) is when eel consumption is at its peak, as it is believed to bring good luck and protection from illness.
Some eel species, such as the European Eel (Anguilla anguilla) and the American Eel (Anguilla rostrata), are classified as "Critically Endangered" on the International Union for Conservation of Nature (IUCN) Red List. The Japanese Eel (Anguilla japonica) and the New Zealand Longfin Eel (Anguilla dieffenbachii) are also considered threatened in their native regions.
The decline in eel populations is primarily attributed to overfishing, habitat loss, and barriers, such as dams and weirs, which obstruct their migratory pathways. Pollution and changes in water quality are additional threats, as eels are highly sensitive to environmental conditions.
Overfishing is a significant threat to eel populations, driven by the high demand for eel meat in many countries, especially in East Asia, where it is a popular culinary delicacy. Catching juvenile eels, known as elvers, for the lucrative eel trade has also contributed to the decline in eel populations.
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Related: To further explore the animal kingdom, check out some of the other animals that start with E.
Miller, M. I., Bonhommeau, S., Munk, P. L., Castonguay, M., Hanel, R., & McCleave, J. D. (2014). A century of research on the larval distributions of the Atlantic eels: a re-examination of the data. Biological Reviews, 90(4), 1035–1064.
Catania, K. C. (2015). Electric eels concentrate their electric field to induce involuntary fatigue in struggling prey. Current Biology, 25(22), 2889–2898.
Miller, M. I., & Tsukamoto, K. (2017). The ecology of oceanic dispersal and survival of anguillid leptocephali. Canadian Journal of Fisheries and Aquatic Sciences, 74(6), 958–971.
Chinny Verana is a degree-qualified marine biologist and researcher passionate about nature and conservation. Her expertise allows her to deeply understand the intricate relationships between marine life and their habitats.
Her unwavering love for the environment fuels her mission to create valuable content for TRVST, ensuring that readers are enlightened about the importance of biodiversity, sustainability, and conservation efforts.
Fact Checked By:
Mike Gomez, BA.