Eel Fish: A Fascinating Group of Elongated Fishes
Eel fish are a diverse group of fishes that belong to the order Anguilliformes, which means “eel-shaped”. They have long, slender bodies that lack pelvic fins and often pectoral fins as well. They have small eyes, a large mouth, and sharp teeth. They can be found in both freshwater and saltwater habitats, and some species can even move on land for short distances.
Eel Fish Lifecycle
One of the most remarkable features of eel fish is their complex lifecycle, which involves several stages of development and migration. Most eel fish are catadromous, meaning they live in freshwater but spawn in saltwater. The only exception is the European eel, which is semelparous, meaning it spawns only once and then dies.
The spawning area for most eel fish is the Sargasso Sea, a region of the Atlantic Ocean near Bermuda. There, the adult eels release their eggs and sperm into the water, where they fertilize and hatch into larval forms called leptocephali. These larvae are transparent and leaf-like, and they drift with the ocean currents for months or even years before reaching their coastal destinations.
As they approach the coast, the leptocephali undergo metamorphosis into a juvenile stage called elver or glass eel. These are small and transparent, and they swim upstream into rivers, lakes, or estuaries. There, they gradually develop pigmentation and become yellow eels or brown eels, depending on the species. These are the mature eels that live in freshwater for several years, feeding on fish, crustaceans, worms, and other prey.
When they reach sexual maturity, the yellow or brown eels change color again and become silver eels. These are the migratory stage that leaves freshwater and returns to the sea to spawn. They stop feeding and rely on their stored fat reserves for energy. They also undergo physiological changes that prepare them for the oceanic environment, such as increased salinity tolerance and gonad development.
The silver eels swim thousands of kilometers across the ocean to reach their spawning grounds in the Sargasso Sea. There, they reproduce and die, completing their lifecycle.
Eel Fish Classification
There are about 800 species of eel fish in 19 families and 111 genera. They are divided into eight suborders based on their morphology and phylogeny. Here are some examples of each suborder:
- Protanguilloidei: This suborder contains only one species, the primitive eel (Protanguilla palau), which was discovered in 2010 in a deep-sea cave in Palau. It has many primitive features that suggest it is a basal lineage of eels.
- Synaphobranchoidei: This suborder includes the cutthroat eels (family Synaphobranchidae) and the spaghetti eels (family Nettastomatidae). They are deep-sea eels that have small eyes, long jaws, and reduced fins.
- Muraenoidei: This suborder comprises the moray eels (family Muraenidae) and the snake eels (family Ophichthidae). They are mostly marine eels that have strong jaws, sharp teeth, and thick skin. Moray eels are often colorful and patterned, while snake eels burrow into sand or mud with their pointed tails.
- Chlopsoidei: This suborder contains only one family, the wolf eels (family Chlopsidae). They are small marine eels that have large mouths and fang-like teeth. They mimic other fishes by hiding their long bodies inside their mouths.
- Congroidei: This suborder includes the conger eels (family Congridae) and the garden eels (family Heterocongridae). They are marine eels that have well-developed eyes, pectoral fins, and lateral lines. Conger eels are large and predatory, while garden eels live in colonies and protrude from sandy bottoms.
- Moringuoidei: This suborder contains only one family, the spaghetti worms (family Moringuidae). They are marine worm-like fishes that have no eyes, scales, or fins. They burrow into sand or mud with their muscular mouths.
- Saccopharyngoidei: This suborder includes the gulper eels (family Saccopharyngidae) and the pelican eels (family Eurypharyngidae). They are deep-sea eels that have enormous mouths, long jaws, and distensible stomachs. They can swallow prey larger than themselves.
- Anguilloidei: This suborder comprises the freshwater eels (family Anguillidae) and the swamp eels (family Synbranchidae). They are mostly freshwater eels that have small scales, dorsal and anal fins that are continuous with the caudal fin, and a swim bladder that is connected to the pharynx. Freshwater eels are catadromous, while swamp eels can breathe air through their skin or mouth.
Eel Fish Uses and Conservation
Eel fish have been used by humans for food, medicine, and cultural purposes for centuries. Some species, such as the European eel, the American eel, and the Japanese eel, are highly valued as delicacies in various cuisines. Eel fish are also used in traditional medicine, especially in Asia, where they are believed to have healing properties for various ailments. Eel fish have also inspired legends, myths, and art in many cultures, such as the Maori of New Zealand, who regard the longfin eel as a sacred animal.
However, eel fish are also facing many threats from human activities, such as overfishing, habitat loss, pollution, dams, climate change, and diseases. Many species are endangered or vulnerable to extinction, according to the International Union for Conservation of Nature (IUCN). Some conservation measures have been implemented to protect eel fish, such as fishing quotas, restocking programs, habitat restoration, and international agreements. However, more research and cooperation are needed to ensure the survival of these fascinating fishes.