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Fire Eel (Mastacembelus erythrotaenia) Care Guide

Last Updated May 18, 2020
Fire Eel Care Guide

If you have a large tropical, freshwater fish tank and you’re looking for something a little different to add to your collection, a Fire eel could be worth considering. However, these fish are not recommended for beginner hobbyists or for those who do not have experience in keeping eels.

In this guide, we introduce you to this exotic-looking species, and we give you all the information that you’ll need to care for one of these enigmatic, imposing creatures.

Fire eel origins

The Fire eel, scientific name Mastacembelus erythrotaenia, is a large variety of spiny eel. Although they look just like an eel in shape and movement, spiny eels are actually a species of freshwater fishes that belong to the same family as Tyretrack eels and Peacock eels.

The Fire eel comes from Southeast Asia, where it’s found in lowland rivers in Myanmar, Pakistan, Sumatra, Laos, Thailand, Burma, Malaysia, and Vietnam. This tropical eel is very popular in the aquarium trade, and it’s also fished for food in its native habitats. For that reason, the numbers of the species are declining in the wild, although Mastacembelus erythrotaenia does not yet appear on the IUCN Red List, and they are readily available to buy for the hobby trade.

In the wild, these tropical eels are bottom dwellers, mainly found in slow-moving rivers and lakes, spending much of their time buried in the muddy substrate, leaving only their snout protruding.

These animals eat a small amount of plant matter, feeding primarily on small fish, insect larvae, worms, crustaceans, and general detritus.

Handle with care

If you take on one of these creatures, you must be very careful if you need to handle the Fire eel.

Although Fire eels don’t generally bite, the fish’s dorsal fin is equipped with spines. The spines are used to protect the fish from attack by predators. Although the spines themselves are not poisonous, the slimy mucus they produce is toxic.

Appearance

The Fire eel is an elongated fish. The creature has a very distinctive, pointed snout, and its jaw is somewhat underslung.

Spiny eels are so-called because of their numerous small spines that run along the creature’s body in front of its dorsal fin. The fish’s body flattens towards the caudal fin to form an extended tail.

The eel’s base color is dark brown to gray on top with lighter shading of the same color on the belly. The body is marked with several bright scarlet lateral stripes and spots. Interestingly, in younger, smaller specimens, these markings are often amber or yellow, becoming deeper in color in larger, more mature animals. The dorsal, pectoral, and anal fins are edged with red.

Underneath the eel’s snout is a sensitive, fleshy outgrowth, which it uses to feel along the substrate, searching for food. This appendage is effectively the eel’s nose, having two tubulated nostrils at the end. Because of that feature, the Fire eel is referred to as belonging to the Mastacembelidae family.

The eel Mastacembelus has an air-bladder, as well as pectoral and tail fins. The dorsal is split into two parts.

Mastacembelus erythrotaenia is the largest species of spiny eel, reaching up to 3.3 feet in length in the wild. When kept in tank conditions, the Fire eel doesn’t generally exceed 20 inches in length. Females are typically larger than males when mature.

Fire Eel Care Guide

Care and maintenance

Although Fire eels are currently in great demand because of their amazing looks, these are not animals to be taken on by the inexperienced, largely because of their very particular aquarium requirements.

Here’s what you need to know if you’re considering buying a Fire eel.

Tank size

The first thing to know is that Fire eels can reach a very large size. So, you must have a tank that will accommodate a full-grown specimen of 20 inches or even more.

The minimum tank size you need is 55 gallons for a juvenile and at the very least 180 gallons for an adult.

All species of spiny eels are proven escape artists, so you must have a tank with a tightly fitting lid and a cover slide. Double-check your setup to make sure that there are no gaps or spaces where the eel could wriggle free, such as cable ports and around inlet pipes.

Tank decoration

Eel Mastacembelus is a confirmed burrower that likes to hide deep in the muddy substrate, so you’ll need to provide your specimen with a thick, sandy substrate of at least 3 inches deep.

These fish love to hide, taking shelter in hollow logs and among thick planting. So, you should include plenty of coarse-leaved and floating plants. Unfortunately, anything planting in the substrate is likely to be unearthed thanks to the eels’ digging habit, but plants that can be trained to grow on pieces of bogwood are a suitable addition to the habitat.

This species of eel is nocturnal, spending the daylight hours hiding under rocks, outcrops, and wood. Therefore, driftwood, terracotta flower pots, PVC pipes, and resin hollow logs all make ideal decorations for the eel’s tank and will provide the animal with what it needs to feel secure and safe. That will reduce stress, making it less likely that the fish will become vulnerable to disease and enabling it to eat well and thrive.

The tank lighting should be kept dim, and you can use floating plants to diffuse the lights if necessary.

Water parameters

Mastacembelus erythrotaenia is found in large lowland river habitats, which makes them not as demanding when it comes to water chemistry as some more habitat-specific species.

Water temperature should be between 75° to 82° Fahrenheit. Water pH between 6.0 and 7.5 is perfect, and the water should be on the hard side at between 6 to 12 dGH.

To maintain good water quality, it’s a good idea to use power filtration and additional aeration to provide good oxygenation levels and reasonably good flow through the tank.

Diet and nutrition

Mastacembelus erythrotaenia can be fed live or frozen food, including bloodworms, small feeder fishes, and tubifex. When your eel becomes larger and older, you may teach it to take food items such as pieces of fish, mussels, earthworms, and chopped or live shrimp.

Generally, the Fire eel won’t eat flake or pellet food, and they rarely take plant matter in captivity.

Often, juvenile specimens can be taught to take food from their owner’s hands. That not only helps to create a bond between you and your pet; it may also help you to monitor the quantity of food that your eel eats each day. Remember that these are nocturnal fish, so you may not actually witness your eel eating unless you adjust the lighting in the tank to create an artificial nighttime environment that enables you to observe what’s happening.

Tankmates

Fire eels can be very aggressive toward their own kind, and, for that reason, they are best kept as a single specimen.

However, you can include a few other large fish species within the tank. Fire eel Mastacembelus erythrotaenia is a shy fish that largely ignores its tankmates. That said, you should not add small fish species to the tank, as they are highly likely to finish up as lunch for the eel.

Suitable tankmates for the Fire eel include Green Terrors, Angelfish, and Oscar fish.

In the wild, these fishes eat invertebrates and crustaceans. For that reason, you should not include snails, shrimp, or crabs in the community.

Breeding

Largely because of their aggressive nature and large size, these fish are difficult to breed in captivity. Therefore, most of the specimens for sale in fish stores and online are generally bred by commercial producers or taken from the wild.

However, if you do fancy a challenge, here’s what you need to know about breeding these remarkable fish.

First, you’ll need to choose a potential breeding pair. Fire eels don’t become sexually mature until they are about two years old. Female fish are generally quite a lot larger than males and slightly paler in color, so sexing them is relatively straightforward. However, if you’re not sure, always ask the dealer or fish store assistant for clarification.

Breeding tank

Once spawning has taken place, you need to remove the parents from the tank so that they don’t eat the eggs or fry. To to that, you’ll need to set up a separate breeding tank.

The spawning tank should be at least 80 gallons and should be set up in the same way as the main display aquarium but without any substrate. You’ll need to keep the tank scrupulously clean by siphoning any uneaten food and waste from the bottom, and a bare tank floor allows you to do that quickly and easily.

The water temperature should be between 82o and 84o Fahrenheit, with a pH range of 7.0 to 7.2, and a water hardness of around 10o. Ideally, you’ll need to position power filters in each corner of the tank to create powerful filtration and boost the oxygen content in the water.

Spawning

To bring the fish into breeding condition, feed them with live bloodworms, tubifex, and insect larvae.

During spawning, the male pursues the female around the tank until she lays her eggs. There will be several spawning sessions over a two day period, during which up to 1,000 eggs will be deposited.

When spawning has finished, remove the parents from the aquarium.

Keep the lighting in the breeding tank at a low level, and carry out a 60% water change. It can also be helpful to add methylene blue to the water to kill off any bacteria that could affect the eggs. The larvae hatch after around 48 to 72 hours, feeding on their yolk sac for the first 12 days or so.

Once the tiny fry becomes free-swimming, you can feed them with baby brine shrimp across five to six small feedings per day. It’s advisable to switch off the filter system to prevent the fry from being injured. Now, you’ll need to carry out 10% water changes every day.

The youngsters grow quickly, reaching around 3 inches by the end of their second month.

Diseases

Unfortunately, most spiny eel fishes are prone to bacterial infections.

The usual cause of health problems in these fish is poor water quality. Once the eel falls sick, it can be extremely difficult to treat it, so it’s up to you to provide your pet with properly maintained water, a clean tank, and the correct diet.

One big cause of infections in Fire eels is a substrate that’s too harsh or abrasive. Sharp gravel or rough sand that has a very coarse grain can irritate the eels’ skin, leading to infection. 

Availability

Some specialist fish stores may have this unusual fish in stock, although you’re more likely to find them advertized by online dealers if you search the internet.

Fire eels are usually priced according to the size of the individual, starting at around $10 for a small example and increasing in cost for larger fish. Remember that you’ll need to account for the cost of shipping too if you buy online, which will push up the cost.

FAQ

In this section of our guide, we answer some of the most commonly asked questions about the Fire eel that are posed by people who are considering taking on one of these beautiful animals.

Q: Are Fire eels dangerous?

A: Mastacembelus erythrotaenia is not dangerous. However, these fish do have sharp dorsal spines, and they secrete a toxic slime, which can be harmful. For that reason, you should avoid handling your eel if at all possible.

Q: Will a Fire eel eat my fish?

A: Fire eels will eat anything that’s small enough to fit into their mouths. For that reason, you must choose your eel’s tankmates carefully.

Q: How long can a Fire eel live out of water?

A: The Fire eel is a fish, not an eel. The animal cannot breathe air, so it will die if it escapes from the tank and is left out of water for longer than a few hours.

Q: How quickly do Fire eels grow?

A: Fire eels grow relatively slowly in captivity at a rate of around four or five inches a year. Once the eels are over a foot long, the growth rate tends to slow down.

In summary

The Fire eel is a fascinating, impressive creature that can make an enthralling centerpiece in any large tropical tank. However, we don’t recommend this species for beginner aquarists, largely due to the animal’s large size and sensitivity to the correct water parameters.

Although you can keep these animals with large, peaceful fish, they can be aggressive with their own kind and will eat smaller fish, invertebrates, and crustaceans.

If you do decide to take on a Fire eel, it’s a good idea to join an online forum where you can search for helpful care tips and troubleshoot problems with fellow enthusiasts, and can also give you a clearer idea of whether one of these freshwater giants would be a suitable pet for you.

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