Fire eel (Mastacembelus erythrotaenia) resembles a true eel, that’s why the fish got its name. However, this fish has nothing in common with eels despite its snake like body and pointed snout. This is a renown tank and commercial fish.
Habitat in the wild
Mastacembelus erythrotaenia dwells in waters of Indonesia, Laos, Vietnam, Cambodia, Pakistan, Burma, Thailand, Malaysia and other countries of South-East Asia. This bottom-dwelling fish is mainly encountered in slow muddy rivers and lakes, since one of its favorite activities is to bury itself in the riverbed.
In Asia locals eat eels, therefore it is highly prized among them. However, young fishermen and aquarists don’t share this attitude because of troubles fire eel gave them with its spines on the dorsal fin.
When being caught the fish tries to escape as fast as possible and it may hurt the one who is holding it with its spines.
Spines themselves are not poisoned, but the slime they produce is toxic. So, if a fire eel has bitten you, hurry up and apply some antiseptic to the wound. But still it is better to be careful with this fish and not to touch it.
Mastacembelus erythrotaenia appearance is like the one of eel. Its elongated body is covered with small scales. The fish has big eyes. Near the anterior border of the fish eye there are its posterior nostrils.
When looking for food fire eel feels the bottom with a sensitive fleshy outgrowth on its snout. At the end of this long nose appendage there are two tubulated nostrils. Due to this peculiarity fire eel is referred to Mastacembelidae family (source).
The fish has well developed air-bladder as well as tail and pectoral fins. The dorsal is divided into two parts. Both anal and dorsal fins are narrow and long and they end near caudal fin.
Red fire eel has no abdominal fins. The coloring is dark brown. There are four bright red or orange lateral stripes along the body, very often they consist of spots and small lines. The color intensity of the spots varies depending of the age and tank conditions. As a rule anal, dorsal and pectoral fins have red edges.
In the wild body size may reach 1 m (3.3 ft), when dwelling in a tank it is 0,5 meters (20 in) long. The lifespan is 10 years and more.
Difficulties in keeping
The fish is rather undemanding, but the fact that this is a predator fish and a large one as well imposes restrictions on keeping it in a tank. You will need at least very spacious tank with tank mates that are large enough, so the fish won’t treat them as food.
Keeping in a tank
|Scientific Name||Mastacembelus erythrotaenia|
|Common Name||Fire eel|
|Tank size||77 gallons and more|
|Diet||Omnivorous bottom feeder|
|Temperature||24-28 °C (75-82°F)|
|Size||up to 1 m (3.3 ft)|
To keep one adult species of the fish you will need a tank larger than 350 liters (77 gallons), with 5 cm (2 in) thick sandy bottom and large number of shelters made of snags, flower pots, bunches of coarse leaved and floating tank plants, that will make the bottom a bit shadowed.
Fire eel adores hiding.
It is likely that you’ll have to forget about tank plants with roots and replace them with floating ones, because fire eel when burying itself in a sandy bottom doesn’t care about about the place, so it is quite possible that the fish will dig some tank plant roots and damage them.
This fish is a nocturnal one. During the day it hides under snags and stones, buries itself in the tank bottom substrate and all you can see is its eyes and a snout.
You should make sure that there are no cracks in the tank, otherwise fire eel will easily ‘escape’ from the tank through the tiniest slit.
Since the fish demonstrates aggression towards its kind, you should keep it alone in a tank but it may have a company of some active and peaceful tank fishes.
Optimal tank water parameters are the following: temperature 24-28 °C (75-82°F), pH 6.8-7.5, water hardness should be not more than 15°. Power aeration, filtration and regular water renew (up to quarter of the total tank volume) is a must when keeping such a fish. It also likes when there is some water flow in a tank.
Compatibility and tank mates
As a rule the fish is timid and it ignores its tank mates, if it can’t eat them; they will eat small fishes though. Fire eel shows aggression towards its king and that’s why it’s not recommended to keep a couple in one tank.
Moreover, there is no point in it, since it is very difficult to obtain the fish eggs.
Mastacembelus erythrotaenia can be hand feed by its owner, whom the fish starts to recognize rather quickly. The fish should be fed with any live food (for example, tubifex, bloodworm, small fishes), dry and frozen food as well.
In the wild this fish is a predator and it preys on insects larvae, worms, snails and even small crabs.
Unlike the male the female one has paler coloring and she is larger than the male.
Fire eel is a very challenging species to breed in captivity, so it is quite a troublesome thing to do. You should use some special hormonal injections, but even after this it doesn’t guarantee that you achieve the anticipated results.
The fish becomes reproductive at the age of two years old. To breed this predator fish in captivity you will need a tank (of 400 liters and more capacity) with a ceramic tube in it or a net stretched over the tank bottom.
The following tank water parameters are optimal for the breeding: temperature 28-29 °C, water hardness about 10°, pH from 7 to 7,2. To create powerful aeration and filtration in the tank you should put four sprayers in different tank corners.
The breeders should be fed with live food: bloodworm, tubifex, insects larvae.
The male haunts the female all over the tank and then catches her near the ceramic tube and squeezes up to 50 yellowish eggs (3 mm in diameter) from the female. In general through the whole spawning period the female lays from 700 to 1000 eggs.
When the spawning is over the fish is removed from the tank. One third of the tank water is renewed with the fresh one, lighting is decreased to its minimal value and the eggs are processed with methylene blue.
The egg stage lasts about 48-72 hours. Larvae except their yolk bag also have a gular sac (presumably in case of oxygen deficiency in water).
In 12 days the larvae starts feeding. Brine shrimp can be used as its first food. Small portions of food should be put in several places of the tank 5-6 times a day.
The juveniles grow fast – during the first month they grow to be about 4.5 cm long and at the end of the second month that are about 7 cm long. When growing juveniles you should turn of the filter to prevent them from getting injured if they get there.
Daily water renew (up to 10%) is a must. As a precaution you should disinfect the water with methylene blue (1-3 mg/l), antibiotics (up to 10 mg/l). Metabolic byproducts as well as food leftovers have to be removed as fast as possible. That’s why tanks without any bottom substrate will be a good idea in this respect.
Juveniles can be also put into ornamental tanks with bottom substrate layer that doesn’t exceed 3 cm. At that you have to turn the bottom substrate at least once in a month.
Using undergravel filters is possible only in case if false bottom is thoroughly fitted and there are not slits. At the age of two weeks the juveniles start getting their coloring – first the spots and lines appear and then the body gets darker.