Freshwater Moray Eel
Gymnothorax polyuranodon
(Bleeker, 1854)
What are they and how big do they get?
G. polyuranodon is better known as the freshwater moray eel, but it also has an array of other common names including freshwater spotted moray, freshwater leopard moray, freshwater tiger moray, many-toothed moray and black spotted moray. It is a species of moray eel belonging to the order Anguilliformes.
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
G. polyuranodon exhibit a catradromous lifestyle, meaning that adult fish live in fresh water and will migrate into salt water to spawn. Young eels (elvers) are born in marine water and will then migrate into freshwater as they develop.
What do they eat in captivity and how often should they be fed?
Usually, they are more than obliging to begin their life in captivity accepting earthworms and dendrobaena worms, but will usually convert onto frozen/thawed alternatives including mussel, prawn and whitebait etc. with relative ease.
Which tankmates are recommended?
Nothing small enough to be regarded as a snack!
Providing that fish are large enough, peaceful and have a preference for similar parameters, tankmate options are plentiful.
The aquarium?
G. polyuranodon is a wallowing (buries itself in the substrate) species that requires an aquarium containing soft sand to allow for this natural behavior.
This species is unrivalled with its ability to escape. It is imperative that the aquarium is secured with a tight-fitting fid, ensuring that even the smallest of gaps have been plugged - you have been warned - this fish is a master of escape!
Will they breed in captivity?
Unlikely, given that an increasing amount of evidence suggests that they are catadromous, thus migrating from rivers (freshwater) to the sea (marine) to breed.
There are no captive breeding reports that we are aware of.
Other notes
The correct care of this species appears to be a topic of debate and whether they're fine to spend their entirety in freshwater alone is an argument that we expect to go on for quite some time.
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 on the eyes and adds bucketloads of interest to the lower levels of the aquarium. However, they do come with an initial cost, but if your pockets are deep enough, you'll be hard-pushed to find an oddball as impressive as this!