Eel

Eels are bony fish, easily recognizable because of their snake-like appearance. They can live in both salt water and fresh water, and certain species migrate between the two, though the first and final stages of their lives take place in the sea. Some fish like the electric eel and deep-sea spiny eels are often mistaken for eels, which are not true eels though. Eeels are also well known for having one of the most unique reproductive cycles amongst all sea life.

List of Common Types of Eel species

Over 800 species of true eels are distributed worldwide, divided into 19 families and about 111 genera. 

Some common freshwater eels: American Eel, European Eel, Japanese Eel

Some common saltwater eels: Conger Eels, Moray Eels

Physical Description and Appearance

Size: They are elongated, ranging from 2 in (5 cm) in length for the one-jawed eel to 157.5 inch (400 cm) for the Slender Giant Moray eel.

One of the longest eel -the American eel- is about 19.7 inches (50 cm), while they are recorded to grow up to 59.8 inches (152 cm)

Weight: An adult eel is between 1 oz (30 g) and 55 lb (25 kg) on average though some can weigh much more. The European conger is the world’s heaviest eel, weighing 240 lb (110 kg).

Color: They appear in a wide variety of colors. Some are monochrome, while others are a mixture of different hues with various patterns like spots and stripes. For instance, the snowflake eel has a white or cream body with black blotches. On the other hand, the zebra moray appears deep brown with yellow or white stripes like the zebra. 

Fins: Eels do not possess pelvic fins, while in some species the pectoral fins remain absent too. Their dorsal, anal and caudal fin fuse together to form a thin ribbon around most of its body.

Distribution

These species can be found in oceans and seas worldwide.

Where are they found

Most eels live in shallow water, though a few can be found in deeper waters, almost up to 13000 ft (4000 m). They may in freshwater habitats like lakes, rivers, and ponds in the beginning, eventually migrating to saltwater locations like seas and oceans when ready to reproduce. However, some, like most Moray eels, live in saltwater throughout their life. 

How long do they live

On average, their lifespan ranges from 15 to 30 years, though some can live for almost 85 years. The longest living eel, the Brantevik Eel, a European Eel species, survived up to 155 years in captivity.

What do they eat

They include small fish, crabs, shrimps, sea urchins, and even other eels. Those living in freshwater even eat larvae of worms and mosquitos. 

Behavior

• They are nocturnal species, with a secretive demeanor.
• Eels swim in a serpentine manner, creating waves as they move. As a result, they can swim backward by simply reversing the direction of the wave.
• While resting, they burrow in the sand or mud on the ocean floor or hide in rocky crevices.
• Their hunting behavior varies. Some will remain hidden and attack prey that passes by, while others chase down and capture their quarry.

Adaptations

• The backbone of these eels is made up of a hundred vertebrae. This allows them to move flexibly.
• They have sharp teeth, allowing them to bite and hold on to prey.
• Some, like the moray eels, come in different colors, often matching with their surroundings, helping them camouflage well and hide from predators. 
• While eels have gills like other fish, they can breathe out of water for hours with the help of their thick skin, which can hold water to prevent them from drying out. 
• Most of them even have mucus coating on their body, helping them move quickly through the rough sea terrain. It even protects them from several underwater organisms like bacteria. 

How do they reproduce 

The reproduction of the eel has remained an enigma, with details about their breeding staying unknown to this day. What scientists have uncovered so far indicates that they mate at the last phase of their lives by forgoing eating altogether and perhaps developing reproductive organs during this period. 

Eels worldwide appear to have specific breeding sites, those from both America and Europe migrating to the Sargasso Sea, Japanese eels to the Suruga seamount, South African eels towards the north of Madagascar in the depths of the Indian Ocean, and New Zealand longfin eels near the nation of Tonga. All of them reproduce, give birth, and finally die.

Life Cycle 

They have a unique life cycle, going through four distinct stages, from an embryo to an adult. The larval stage of the eel, known as leptocephali, is transparent and flat. They drift about in the sea, eating marine snow for nourishment until they mature into glass eels. This stage travels from saltwater to freshwater, though some remain in the ocean for their entire lives. They then reach their 3rd stage, the elver as young eels are called, and begin moving further upstream. After becoming fully mature, they stay in their freshwater habitats until they return to the seas to breed.

Conservation

Due to being a high-demand delicacy in Europe and Asia, the population has fallen drastically since the 19th century. The Japanese consume over 70% of the global catches. This has led to conservation efforts to prevent their numbers from declining further. Greenpeace International added the American eel, the European eel, and the Japanese eel to its red list of seafood species in 2010.

Eel – FAQs

Interesting Facts

• Garden eels live on the seafloor and can be seen poking out of the sand, looking like grass.
• They have poor eyesight and need to rely on their other senses to move about.
• Elvers, once commonly available in the UK, were a cheap source of food. However, they were overfished and over consumed to the point of extinction and are now considered a rare delicacy.
• Eel fishing and consumption are major plot points in certain literary works like Günter Grass’ The Tin Drum and Jo Nesbø’s The Cockroaches.