This fish looks like an eel, but it is not a moray or conger eel. There is a fish known as a wolf fish that is actually a gigantic blenny-type fish. But what about the wolf eel? What the heck is it? It turns out that this unusual fish is most closely related to a dottyback (family Pseudochromidae). The wolf eel is one of at least a dozen species in the subfamily Congrogadinae. All the species in this genus are more eel-like. Many members of this subfamily are referred to as snakelets. Probably a better, less confusing name for the wolf eel is the carpet eel snakelet.
Difficulty: The wolf eel is a very easy fish to keep. The wolf eel is disease-resistant and only needs to be fed every other day or so. You should give the wolf eel chunks of meaty foods, like chopped frozen seafood and krill. The wolf eel is said to eat crustaceans and small fish in the wild.
Physical description: The wolf eel is snakelike in form with a snarly under bite. The wolf eel can be brown or green overall with varying degrees of lighter mottling and blotches. The wolf eel can change color to better match its background, or it may change colors when threatened. This fish can become very pale overall, a color pattern they often adopt at night. Some have suggested that Congrogadus subducens is sexually dichromatic, but this does not appear to be the case. There is some evidence that male wolf eels are usually larger than female wolf eels.
Range: Nicobar Island in the Indian Ocean east to Papua New Guinea, south to northwestern Australia and north to the Ryukus. The wolf eel occurs in lagoon seagrass beds and lagoon and tidal rubble flats and is typically found in very shallow water (less than 10 feet and often in tide pools of less than a foot).
Compatibility: The wolf eel is a voracious predator that will eat any small fish kept with it. It may even snap at larger fish that swim by when it is aroused by the presence of food. The best tankmates for the wolf eel are larger species, such as squirrelfishes, soldierfishes, angelfishes, butterflyfishes, surgeonfishes and rabbitfishes. The wolf eel can also be kept with more placid morays, though larger species (e.g., honeycomb moray, Gymnothorax favagineus; spotted moray, Gymnothorax moringa) have been known to eat Congrogadus subducens. It is prudent to keep only one wolf eel per aquarium, as conspecifics will fight and may bite and chase each other until one of the combatants is dead. The wolf eel will eat ornamental crustaceans, but is no threat to corals or most other invertebrates.
Aquarium conditions: The wolf eel can be kept in aquariums of 20 gallons or more. In fact, it is a wonderful fish for the smaller species aquarium. The wolf eel aquarium should include numerous hiding places. It is likely that the wolf eel will dig under aquascaping and may topple unstable rockwork. The aquarium water parameters should be a pH of 8.1 to 8.4, specific gravity of 1.019 to 1.025 and a water temperature of 74 to 82 degrees Fahrenheit.
Care considerations: The wolf eel must be kept in an aquarium that has a secure top, as it is prone to leaping from open aquariums.
Breeding: The wolf eel has been known to spawn in captivity, but sexing them can be difficult. Wolf eels may be hermaphrodites, so selecting individuals that differ in size may increase the chances of getting a heterosexual pair. (If the size difference is too great, the larger fish may eat the small conspecific.) The female wolf eel will build a nest by sweeping substrate away with her tail. This is usually done under a rock or aquarium decor. The female wolf eel will deposit a pink or purplish egg mass in the “nest” depression that contains from 50 to 100 eggs that are about 3 to 4 mm in diameter. After depositing the eggs, the female wolf eel will wrap her body around them and regularly fan them by undulating her dorsal and anal fins. She will protect her eggs from the male wolf eel and other fish in the aquarium. (It may be a good idea to remove the male wolf eel, as he is likely to eat the eggs or be damaged by the female wolf eel!) The young wolf eels are relatively large at hatching and are relatively easy to raise. They are reported to take enriched baby brine shrimp.