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Eels: The Elongated Fishes of the Ocean and Freshwater


Eels: The Elongated Fishes of the Ocean and Freshwater

Eels are a group of ray-finned fishes that belong to the order Anguilliformes, which means “eel-shaped”. They have long, slender, scaleless bodies that lack pelvic fins and can move easily through narrow spaces. Eels are found in both salt and fresh water, and some species migrate between the two environments to reproduce. Eels are diverse and fascinating animals that have many adaptations for their lifestyles.

Description

Eels vary in size, color, and shape depending on their species and habitat. The smallest eel is the deep-sea Cyema atrum, which measures only 10 cm (4 inches) long, while the largest is the moray Thyrsoidea macrura, which can reach up to 3.5 meters (11.5 feet) long. Eels can be drab gray or black in deep-sea species, or colorful and patterned in tropical reef species. Some eels have sharp teeth and strong jaws for catching prey, while others have small mouths and feed on plankton or detritus. Some eels have electric organs that can produce shocks for defense or hunting, while others have venomous spines or glands that can inflict painful wounds.

Lifecycle


Description

Eels have a remarkable and complex lifecycle that involves several stages and migrations. Eels begin their lives as eggs that are fertilized in the open ocean, usually in warm tropical or subtropical waters. The eggs hatch into leaf-like larvae called leptocephali, which drift with the ocean currents for months or years before transforming into glass eels, which are transparent and resemble adult eels. Glass eels then migrate to coastal or freshwater habitats, where they become elvers, which are pigmented and start to feed actively. Elvers grow into yellow eels, which are the juvenile stage that can last for several years. Yellow eels eventually mature into silver eels, which are larger, darker, and more streamlined. Silver eels then migrate back to the ocean to spawn and die.

Classification


Lifecycle

Eels belong to the order Anguilliformes, which consists of eight suborders, 19 families, 111 genera, and about 800 species. The most familiar eels are the freshwater eels of the family Anguillidae, which are widely distributed and valued as food in many cultures. Other eel families include the morays (Muraenidae), which are mostly marine and have powerful jaws and teeth; the congers (Congridae), which are also marine and have large eyes and long dorsal fins; the gulpers (Saccopharyngidae), which are deep-sea predators with huge mouths; and the electric eels (Electrophoridae), which are freshwater fishes that can generate electric shocks. Eels are not closely related to other fish groups that have eel-like shapes, such as lampreys, spiny eels, swamp eels, or deep-sea spiny eels.

Use by humans


Classification

Eels have been used by humans for food, medicine, and cultural purposes for centuries. Freshwater eels are especially prized as delicacies in many regions of the world, such as Europe, Asia, and Oceania. Eel meat is rich in protein, fat, vitamins, and minerals. Eel skin is also used for leather products or as a source of collagen. Eel blood has been used as a medicine for various ailments in traditional Chinese medicine. Eel bones have been used as needles or tools by some indigenous peoples. Eel fishing has been an important economic activity for many communities, but also poses threats to eel populations due to overexploitation, habitat loss, pollution, and climate change. Eels have also inspired legends, myths, art forms, and scientific discoveries throughout history.

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