Freshwater Moray Eel
Gymnothorax polyuranodon
(Bleeker, 1854)
What are they and how big do they get?
G. polyuranodon, commonly known as the freshwater moray eel, is also referred to by several other names, including the freshwater spotted moray, freshwater leopard moray, freshwater tiger moray, many-toothed moray, and black spotted moray. This species is part of the order Anguilliformes and is classified as a moray eel.
Wild fish can attain a size of around 60 in (152 cm), but in captivity, a size of around 36 in (91 cm) is to be expected.
What temperature can they be kept at?
This species is tropical and should be maintained at a temperature within the region of 24-28 °C (75-82 °F).
How many can be kept together?
In a spacious aquarium, they can be kept as a group, but many aquarists choose to keep them singularly.
Water parameters?
pH - 7.5 - 8.2
dH - 8-25 degrees
The freshwater moray eel exhibits a catadromous lifestyle, meaning that adult fish live in fresh water and migrate back to sea to spawn. Young eels are known as elvers; they're born at sea and then migrate into freshwater as they develop.
What do they eat in captivity and how often should they be fed?
Unsettled fish can be encouraged to feed by offering earthworms or dondrobaena worms initially. However, once settled, frozen/thawed alternatives, including mussels, prawns, whitebait, etc., are usually accepted.
Which tankmates are recommended?
The freshwater moray eel can make a fantastic addition to a carefully chosen community, and tankmate options are plentiful. However, it is crucial that tankmates are large enough to avoid being eaten and that they are peaceful.
The aquarium?
The aquarium should have a soft sand substrate, as this provides freshwater moray eels with a comfortable environment to wallow and search for food.
This species is exceptional in its ability to escape. It is crucial that the aquarium be fitted with a secure lid, guaranteeing that even the tiniest gaps are sealed—you have been warned—this fish is a true escape artist!
Will they breed in captivity?
It is unlikely, as increasing evidence indicates that they are catadromous, meaning they migrate from rivers (freshwater) to the sea (marine) to breed. We are not aware of any reports on captive breeding.
Other notes
The care requirements for this species are a subject of ongoing debate. There is considerable discussion regarding whether this fish can thrive solely in freshwater or if it requires the ability to migrate to saltwater.
However, a study (Allen, 1991; Böhlke and McCosker, 2001; Marquet et al., 2003; Jenkins et al., 2009; Ebner et al., 2011, 2016) was conducted and tested to see if G. polyuranodon can co-exist, survive and grow in freshwater over an extended period of time. The results showed yearly growth in length of 21 - 26.5 cm and body mass of 2.4-3.9 times, suggesting that this species may well be long-term riverine inhabitants during adulthood.
(ref: https://en.wikipedia.org/wiki/Gymnothorax_polyuranodon).
Conclusion
This fish is a real treat for the eyes. They do come with an initial cost, but if your pockets are deep enough, you'll be hard-pressed to find a more impressive oddball!