The "Freshwater" (Brackish to Marine) Moray Eels, Family Muraenidae
Bob Fenner
Of the fifteen genera and more than two-hundred species of muraenids there are a couple of handfuls that are known to occasionally enter freshwater in tropical and temperate areas. Of these, two are of principal use to aquarists, being available in good numbers in areas where regular collection of ornamentals is an industry.
The purpose of this article is to inform the public and industry that these two species are really not so much "permanent" freshwater residents... but better considered brackish water organisms (spg 1.005-1.010). Though you may see them presented in "all freshwater settings" for sale, they are best kept in partially saltwater as long term possibilities.
Other literature-noted marine, venturing into brackish, possibly freshwater Morays are listed, and a smattering of non-moray anquilliforms (true eels), as is a mention of a few of the many groups of fishes called "eels" that are not true eels.
Most notably more Freshwater to Brackish:
Echidna rhodochilus Bleeker 1863, "Freshwater White-Cheeked Moray". Indo-west Pacific; Indonesia and Philippines. To about thirteen inches in length... this is principally a marine species, consider it temporarily brackish. It occasionally enters freshwater... Aquarium image. Generally only accepts live shrimp, small fishes as foods.
Gymnothorax polyuranodon (Bleeker 1853), a "Freshwater Moray". Indo-Pacific; Sri Lanka to Fiji, down to Australia. To about three feet in length... if it lives... most do not... this is a freshwater to brackish to marine/estuarine species. Best considered brackish. Aquarium image of a Philippine specimen (Fiji, New Guinea ones black and white mottled). Easily fed on all fresh or live meaty foods.
Other Morays that venture from Marine into Brackish to and Maybe into Fresh For A While (Temporarily): Rare in ornamental aquatics.
Anarchias seychellensis Smith 1962, the Seychelles Moray Eel. Indo-Pacific; East Africa to Easter Island. To nearly a foot in length. Brackish to marine.
Echidna leucotaenia Schultz 1943, the White Faced Moray Eel. Indo-Pacific; East Africa to the Tuamotus. To thirty inches. Brackish.
Gymnothorax afer Bloch 1795, the Dark Moray. Eastern Atlantic; Mauritania to Namibia. To a meter in length. Brackish to marine.
Gymnothorax fimbriatus (Bennett 1832), the Fimbriated Moray. Indo-Pacific; Madagascar to the Society Islands. To thirty two inches in length.
Gymnothorax tile (Hamilton 1822). Indo-West Pacific; Andaman Sea to Indonesia, Philippines. To two feet total length.
Strophidon sathete, Hamilton 1822 is almost certainly the same species), the Giant Slender Moray Eel. Indo-Pacific; Red Sea, eastern coast of Africa to Fiji. To twelve feet in length.
Thyrsoidea macrura (Bleeker 1854), the Giant Slender Moray Eel. Indo-Pacific; Red Sea, eastern coast of Africa to Fiji. To more than thirteen feet in length (world's largest moray). Found around river mouths, occasionally entering into freshwater. A food fish that is rarely offered in the pet-fish trade. A voracious feeder on fish, shrimp, cephalopods.
Uropterygius concolor (Ruppell 1838), the Unicolor Snake Moray. Indo-Pacific; Red Sea, East Africa to the Society Islands. To twenty inches in length. Brackish to marine, often found in Mangrove swamps.
Uropterygius micropterus (Bleeker 1852), Tidepool Snake Moray. Indo-Pacific; East Africa to Samoa. To a foot long. Brackish to marine.
Other True Eel Families with Members that Live in Brackish to Freshwater Settings:
More Anguilliform families with freshwater to brackish members: Moringuidae (Spaghetti Eels), Ophichthidae (Snake and Worm Eels, Myrichthys breviceps at right).
Other Freshwater to Marine True Eels (Order Anguilliformes, that turn up occasionally in the hobby).
Anguillids, family Anquillidae. One genus, fifteen species of mostly catadromous (living in freshwater as young to adults, moving to the sea to reproduce, perishing there) fishes:
Anguilla anguilla (Linnaeus 1758), the European Eel, at the London Aquarium. Anquilla rostrata, occasionally offered for sale in the United States, is very similar.
And of Course, the MANY Marine and Freshwater "Eels" That Are Not Really Eels:
Family Anarhichadidae, Wolf fishes, Wolf Blennies, Wolf Eels; North Atlantic, North Pacific. Two genera with four species. These neat, hand-trainable fishes are mainly seen in public aquaria as they can be enormous (up to 2.5 meters) in size. Gentle giants that are favorites of Public Aquariums everywhere. An Anarrhichthys ocellatus at the Birch Aquarium, San Diego.
Eelblennies, the subfamily Congrogadinae, family Pseudochromidae. Yes, the same family as the Dottybacks... The most commonly offered Eelblenny (aka Green Wolf Eel) in the hobby, Congrogadus subduscens (Richardson 1843) is shown at right.
Spiny Eels (true eels lack spines in their fins), the Mastacembelids. Found in Africa, through Syria, the Malay Archipelago and China. Four genera, sixty seven species. A Fire Eel, Mastacembelus erythrotaenia at right for example.
Swamp Eels, the family Symbranchidae. Tropical and subtropical freshwater, some into brackish environs. Western Africa, Asia, Indo-Australian Archipelago, Mexico and South America. Four genera, fifteen species. One Swamp Eel (Monopterus alba) is often referred to as a/the Freshwater Moray Eel in the aquarium trade.
Are there more? You betcha. Eelcods, Eelpouts... but these others are rarely seen in the hobby.
As you can appreciate, many fishes are capable of short-term exposure to conditions that are deleterious in longer time frames. All living things have their tolerance outside of "ideal ranges" of pH, hardness, dissolved oxygen and such. Salinity is another of the possible categories of such tolerance. Hobbyists and dealers in the trade would do well to impress on each other the need for some salt in the water of "freshwater morays", as well as sufficient alkalinity, elevated pH.
The "typical" aquarium care of Morays applies to the partially, temporarily brackish to freshwater species. They're mainly nocturnal, great at escaping captivity, need large quarters, with places to hide, not too-bright lighting, and are capable of eating slow, small fishes, crustaceans...
