The freshwater habitats of New Zealand are home to the New Zealand Longfin Eel. These eels can grow up to 6.6 feet long, with females reaching this maximum size. Hence, the New Zealand Longfin Eel is one of the world’s largest eel species. 

These eels are olive green to brown. Their long dorsal fins are notable features; they undulate gracefully, helping them move quietly during nocturnal hunts. Despite their size, they are shy creatures.

During the day, they hide in shadowy locations, such as submerged logs or unseen crevices. Their keen sense of smell helps them find prey, primarily invertebrates, small mammals, and other fish.

Moreover, these eels can live for over a century but only breed once. During the breeding season, they embark on an epic journey from their freshwater homes to their spawning grounds in the deep Pacific Ocean near Tonga. After mating, the eels die. Then, thousands of minute larvae return to New Zealand, guided by the waves.

The speckled longfin eel, Australian long-finned eel or marbled eel (Anguilla reinhardtii) is one of 15 species of eel in the family Anguillidae. It has a long snake-like cylindrical body with its dorsal, tail and anal fins joined to form one long fin. The dorsal fin also often extends farther than the anal fin. It usually has a brownish green or olive green back and sides with small darker spots or blotches all over its body. Its underside is paler.[2] It has a small gill opening on each side of its wide head, with thick lips. It is Australia's largest freshwater eel, and the female usually grows much larger than the male.[2][3] It is also known as the spotted eel.

The Southern Shortfin Eel typically inhabits cooler freshwater areas in Australia, New Zealand, and Tasmania. This species is dark brown and olive green, with a lighter underbelly and a shorter dorsal fin. Due to their snake-like locomotion, they can briefly go on land.

The Southern Shortfin Eel also starts life in the deep Coral Sea, turning from larvae into transparent glass eels. Braving numerous challenges, these eels journey from their birthplace to freshwater habitats. Female eels are larger than males, growing up to 3.3 feet long.

These types of eels prefer to stay hidden during the day under rocks and vegetation. They are active at night, feeding on fish, crustaceans, insects, and worms.

The purple spaghetti-eel[2] (Moringua raitaborua) is an eel  in the family Moringuidae  (spaghetti/worm eels).[3] It was described by Francis Buchanan-Hamilton in 1822, originally under the genus Muraena.[4] It is a tropical eel known from India, Bangladesh, Nepal, Indonesia, and the Philippines. It inhabits rivers  and estuaries (including ones in West Bengal, linked to the Ganges River), and has adapted to rapid and wide changes in salinity, pH, and osmoregulatory and hypoxic conditions.[5] Males can reach a maximum standard length of 44 cm.

Snake eels or worm eels look like snakes with long bodies and a scaled texture. They range in color from brown to bright hues and often have patterns serving as camouflage. They live in marine, brackish, and sometimes freshwater environments and spend most of the day burrowed in sand or mud. 

This type of eel has a forward escape technique—they disappear by moving forward, not backward, into the sand. Additionally, their hard, pointed tails are uniquely adapted for burrowing. These traits showcase the fascinating adaptability of life underwater.

Pike conger eels can live in fresh and saltwater environments, although they typically prefer saltwater. These eels can grow from two to eight feet long and survive depths of up to 2624.67 ft.

Approximately fifteen different species of pike conger eels live around the world.

Sawtooth eels are pelagic fish living in the dark depths of the ocean. Their name comes from their inward-facing saw-like teeth. This type of eel comprises around eleven species; most sawtooth eels have a maximum size of 24 to 28 in.

Growing up to 5 feet, this long, slender eel moves quickly through the rocky reef environment. The Mediterranean Moray Eel ranges from dark brown to soft grey, with a yellowish underbelly. It doesn't have pectoral fins.

This eel feeds on fish, squids, and octopuses. However, it's far from the top of the food chain as larger fish and marine mammals like seals and sea lions also prey on them.

Moreover, the Mediterranean Moray Eel forces water over its gills to breathe, requiring it to open and close its mouth rhythmically.

The Giant Moray Eel lives in the Indo-Pacific region's rocky seafloors and coral reefs. It is the world's largest moray eel, measuring 10 feet and weighing over 66 pounds. (The Slender Giant Moray Eel is longer.) Its brown skin has a unique dark spot pattern contrasting with the colorful reefs.

Moreover, this nocturnal eel hides in crevices and caves to avoid predators and rest for its nighttime hunts for fish, cephalopods, and crustaceans. 

The Giant Moray Eel also forms alliances with coral groupers to hunt prey. It chases prey into open waters while the grouper takes advantage.

The California Moray Eel lives in the moonlit kelp forests of the eastern Pacific. Their color palette ranges from bronze to olive green and can grow up to 60 in long, although most average around 24 in. Despite their size, they are shy and spend their days hidden in rocky alcoves, away from other marine life.

At nightfall, the California Moray Eel becomes active and relies on its sense of smell to locate small fish or various invertebrates. It creates a cloud of slime to trap and paralyze its victim against the reef or kelp.

Additionally, the eel starts life as a female and becomes a male as it matures through a phenomenon called protogyny. 

The California Moray is a primarily solitary species that mainly interacts with others during mating.