So Fire Eel

The fish we commonly call the Fire Eel and less frequently the Spotted Eel or Spotted Fire Eel (Mastacembelus erythrotaenia) is a member of the family Mastacembelidae, more commonly called Spiny Eels. In addition to their very cool body shape, they're a gorgeous fish, with a combination of red stripes and spots. At full maturity, the largest specimen we know if got to a somewhat shocking 40 inches long! This length qualifies it as one of the largest species of Spiny Eel!

M. erythrotaenia is a common fish throughout Southeast Asia, generally found in areas where there is slow moving water like swamps, backwaters and the slowest of rivers. The water in these areas is frequently murky and as a result, good displays for these fish are also frequently dimly lit or feature floating (and other) plants to cut down on the light. Fire Eels need fine, soft substrate, sand with sharp edges and rough gravel can injure them. This species is a burrower and will move substrate around as it hunts for inverts and new places to hide in the tank. They're unlikely to bother your plants intentionally, but as a result of the burrowing and rooting behavior, may inadvertently uproot anything planted directly in the substrate. You can get around this by choosing plants that are either in planters or affixed to other aquarium décor like smooth driftwood and rocks.

As we referenced earlier, Fire Eels get big, and so when it comes to aquariums, you should plan for a correspondingly big tank right from the get-go. We suggest nothing less than 120 gallons for one at adulthood. These tanks should emphasize footprint over depth, they'll appreciate more horizontal space over vertical space. Any tank that is home to a spiny eel should be tightly covered as they are the Harry Houdini's of the aquarium world and can easily end up on the floor. They are even more likely to escape if their display doesn't have adequate cover or substrate as they'll go looking for greener pastures, and it turns out that the tank on the other side of the glass never has greener grass.

Most of you reading this have heard the word “nocturnal” and if you haven't, it just means active at night. There is another neat term for animals that are active during low light hours like early dawn and late dusk and this word is crepuscular. Fire Eels qualify as both, making it even more important to give them plenty of hiding places, lots of soft sand and shelter from bright lighting if you want to see them often. Once this Spiny Eel settles in and gets used to feeding times that happen during daylight, you'll see it much more frequently. If after a few days it is still hidden most of the time, it might be a sign that they'd like you to turn down the lights or offer them more cover. The safer they feel, the more you'll see them.

These feeding times are critical as far as training your Fire Eel, start by getting them food at night, early morning or late evening (remember crepuscular?). This schedule will ensure your fish is getting food when it wants it. As pretty much all the Mastacembelus erythrotaenia available to the home aquarist are wild caught, they're going to take some time to adjust to a daylight feeding schedule. You can slowly adjust these feedings to later in the morning and earlier in the evening until they are active enough to feed during daylight. Once this happens, they are relatively easy to train to take food directly from tongs or for the bolder of you, even your hands. We don't recommend this, and don't come complaining to us when you get bit (which is actually pretty unlikely as they have very small mouths).

In the wild, these fish are insectivores. Yes, that's right, they eat mostly bugs, but terrestrial and aquatic. To answer a question some of you may have: yes, there are tons of bugs that live their whole lives underwater as well as many that live the vast majority of their lives underwater only hatch out one day and finish out their existence as airborne things like dragonflies, mayflies and stoneflies. In regard to feeding your Eels at home, they'll relish foods like Gamma Bloodworm, Blackworm, Mysis, and Tubifex among others. They'll also relish live foods, and this is a good way to get them started feeding if you're having difficulty. Small red worms and meal worms or grubs are usually greedily accepted as well as live feeder shrimp and even things like crickets. Most small Fire Eels will relish eating Brine Shrimp, but this is not a nutritious enough meal to sustain the Eel long term. While they exist mostly on insects, they are also opportunistic and won't hesitate to eat a small, unwary fish like clean feeder guppies.

There are reports of home and professional hobbyists getting Mastacembelus erythrotaenia to reproduce in captivity, but little is understood about this. Most of the incidents of this happening are accidental where it has happened in really big tanks, with very large fish. The males and females can be differentiated as the males are usually smaller and more brightly colored, and females in breeding condition will noticeably plump up. The real difficulty in getting this done with any reliability is that Fire Eels are generally fairly aggressive with each other (and other similarly shaped fish), so having two in the same tank that don't want to fight usually requires a massive aquarium.

The wild environment these are found it naturally have a variety of water quality parameters. Generally, Mastacembelus erythrotaenia likes a tank that is slightly acidic, so choose a pH between 6 and 7, and keep it warm, we suggest a tank temp between 75- and 82-degrees Fahrenheit. They should be fine in all but the softest water. Keeping the nutrient levels low will help them stay nice and healthy, so don't skimp of filtration or water changes. Fire Eels are gorgeous, unique, intelligent and mostly peaceful fish that could be kept on their own as they are definitely cool enough to be worth a tank to themselves. Conversely, you could keep them in a community tank with a wide variety of fish. Fire Eels are pretty likely to ignore just about anything they can't eat, and the only other problem here would be fish that pick on them. Fire eels (like many Mastacembelus) can be prone to infections if they get injured, (which is why the fine sand and smooth décor is so important) so avoid fish like barbs that are notorious nippers and stay away from very aggressive fish as well. Offer your Fire Eel lots of hiding places, a safe and securely covered aquarium, plenty of appropriate food, and you'll keep a fascinating wet pet for years to come! If this sounds like something you're interested in, ask your Local Fish Store about getting you a sustainably sourced Mastacembelus erythrotaenia from Aquatropic!