Freshwater Eels and Eel-like Fishes

   Fish referred to as 'Freshwater Eels' in the aquarium hobby and included here belong to various families.

   The True Eels in the order of Anuilliformes includes Freshwater Eels in the family Anguillidae and the Worm or Spaghetti Eels in the family Moringuidae.
   Spiny Eels in the family Mastacembelidae are not actually eels but surely they look like them, as do the Swamp Eels in the family Synbranchidae.
   Then there is the well known Electric Eel. The Electric Eel is also not a true eel, as it belongs to the family Gymnotidae, or Naked-backed Knifefish, but we are including it here because of its common "Eel" name.

Description:
   Fish that are called 'eels' have a long snake-like body. Most are without a separate dorsal and pelvic fin, rather their fins appear merge together with the tail fin to form a continuous fin fringe. Most also have small gill opens, often just a single gill slit at the throat. Eels vary in size but the average size of most species is from between 12" to 36" (30 - 90 cm) long. Many of these fish are only suitable to a home aquarium as juveniles because as adults they simply become too large. The life span also varies depending on the individual species.
   In their native regions many of these fish are considered a good tasting food.

Care and feeding:
   Eels and eel-like fish are mostly carnivores. They mainly get active in the evening or after dark and are mostly bottom feeders. Primarily they will eat live food such as small crustaceans, mosquito larvae, worms, and fish. Some of these fish, such as the Spiny Eels and the Freshwater Eels, are also carrion eaters and may adapt to eating freeze dried and frozen proteins such as tubifex and bloodworms. Eels only need to be fed a couple of times a week and some may refuse food offered that often, eating only once every two or three weeks.
   Generally quite hardy, eels and eel-like fish adapt to most aquarium conditions. For the most part these fish are bottom dwellers, but many species are able to breathe air at the surface directly from the atmosphere. Some eels are great jumpers and most of them are excellent escape artists, getting through any available hole in the aquarium cover. Being both jumpers and able to breathe air, Swamp Eels have been known to cross great distances of land.
   Eels like to hide in caves or holes but also need plenty of space to swim. Many species, especially the Spiny Eels, also enjoy burrowing into the substrate. Because most eels are naked or have very small scales protecting their bodies it is important that the substrate is soft, such as fine sand and peat. They do best in a dimly lit aquarium or one with floating plants to help subdue the light.
   Though most eels can be kept together as juveniles they may become quarrelsome if they are over crowded. They become aggressive solitary predators as adults and will eat smaller and slower moving fish. They should only be kept with species of a similar size.

Breeding:
   There is little known about the reproduction of most of these fish and they are not currently bred in captivity.
   Two Freshwater Eels in the Anguillidae family available to aquarists, the European Eel Anguilla anguilla and the American Eel Anguilla rostrata (the only true eel in North America), live in fresh water but spawn in the ocean.
   The Swamp Eels in the family Synbranchidae are often found in swamps and ponds. They spawn in shallow waters, laying hundreds of free floating eggs that gather together in bubbles.