The Zig Zag Eel is a long time aquarium favorite, and it has been known for over 200 years!
The Zig Zag Eel Mastacembelus armatus has a very long history. It was recognized and described over 200 years ago by Lacepède in 1800. It has been a favorite spiny eel kept by aquarium enthusiasts for many years. Some other common names for this eel include Tire Track Eel, Spiny Eel, White-Spotted Spiny Eel, Marbled Spiny Eel, Giant Spiny Eel, Giant Mottled Eel, Car Track Spiny Eel, and Leopard Spiny Eel.
This fish is not considered to be a true eel, but like all members of the Mastacembelidae family, known as the Spiny Eels, its body shape is definitely eel-like. It is very cute little fish when it is first acquired. It has an elongated body and a long snout, and is generally about 4 inches long. But be aware that this fish will grow, and could reach close to 3 feet in length. An adult will require a very large aquarium.
The popularity of the Zig Zag Eel M. armatus is rivaled by its similar looking relative, the Tire Track EelMastacembelus favus. These eels are recognized and named for their distinct, irregular dark black markings. They both have ‘tire track’ or ‘zig zag’ type markings and both bear the common names of Zig Zag Eel and Tire Track Eel.
The term “tire track eel’ can get rather confusing, There are actually several spiny eels that are called Tire Track Eels, and so are often mis-identified. This is a common name that is used for 3, sometimes 4 different species. Besides being used for M. armatus and M. favus, it is also a common name used for the Half-banded Spiny EelMacrognathus circumcinctus, and occasionally for the Black Spotted EelMastacembelus dayi.
The two popular two spiny eels M. armatus and M. favus, are also often ms-identified because they are so similar looking when offered for sale as juveniles. But despite their very similar appearances, they do have some recognizable differences. Overall their coloration is quite similar, but the placement of the reticulated patterning on the body is the most distinguishing element.
The Zig Zag Eel M. armatus discussed here has a series of irregular dark markings along the entire length of its body. But the reticulated patterning is strong on the upper two thirds of its body, leaving the lower belly portion mostly plain. Its relative M. favus is also marked along the entire length of its body, but its patterning is more extreme. The irregular markings on M. favus reach from the top of its back down through its belly.
Of these two Spiny Eels, the Tire Track Eel M. favus is perhaps the more frequently imported. Though it’s difficult to tell them apart, it is important to know which of these two Spiny Eels you are getting so you can prepare for their long term care. Besides patterning discussed above, there is another primary difference between these two that is not readily apparent when purchasing. That is their adult size. The Tire Track Eel can get up to about 28 inches (70 cm) long while this eel, the Zig Zag Eel M. armatus, will ultimately be quite a bit larger. It can reach up to 35 inches (90 cm) in length, though in the aquarium they usually won’t grow much more than 20 inches (51 cm).
For Information on keeping freshwater fish, see:
Freshwater Aquarium Guide: Aquarium Setup and Care
- Kingdom: Animalia
- Phylum: Chordata
- Class: Actinopterygii
- Order: Synbranchiformes
- Family: Mastacembelidae
- Genus: Mastacembelus
- Species: armatus
- Aquarist Experience Level: Intermediate
- Size of fish – inches: 35.4 inches (89.99 cm)
- Minimum Tank Size: 100 gal (379 L)
- Temperament: Semi-aggressive
- Aquarium Hardiness: Moderately Difficult
- Temperature: 72.0 to 82.0° F (22.2 to 27.8° C)
- My Aquarium – Enter your aquarium to see if this fish is compatible!
Habitat: Distribution / Background
The Zig Zag Eel Mastacembelus armatus was described by Lacepède in 1800. They are found in Asia: Pakistan to Viet Nam and Indonesia.This species is listed on the IUCN Red List as least concern (LC) because it is widely distributed, although harvested by fisheries and for the aquarium trade, there is no significant threats identified at present. They are used as a food fish in their native countries. Other common names they are known by are Tire Track Eel, Spiny Eel, White-Spotted Spiny Eel, Marbled Spiny Eel, White Spot Spiny Eel, Leopard Spiny Eel, Giant Spiny Eel, Car Track Spiny Eel, and White-spotted Car-track Eel.
They are found in moving waters, such as rivers and streams with sandy to pebbly bottoms, normally with dense with vegetation. They also inhabit still waters in coastal marshes and may migrate during the dry season into canals, lakes and floodplain areas. They are nocturnal and will sometimes partially bury themselves in the substrate during the day, coming out at night to feed on at night on benthic insect larvae, worms and some submerged plant material.
- Scientific Name: Mastacembelus armatus
- Social Grouping: Solitary
- IUCN Red List: LC – Least Concern
The body of the Zig Zag Eel is elongated with a long snout. Both the dorsal and anal fins are extended and joined to the caudal fin. These fish can reach just over 35 inches (90 cm) in length in the wild, though they will not generally exceed about 20 inches” (51 cm) in captivity. Spiny eels have a lifespan of 8-18 years.
Its background coloration is a tan to light brown and it has a dark horizontal stripe running through the eye. Along the entire length of its body, reaching vertically from its back to its belly, it is patterned with a series of irregular dark markings. These markings generally have a ‘tire track’ or ‘zig zag’ appearance which has been used as a common name for this fish as well as several other species of spiny eel.
This fish should not be confused with its very similar looking relative, the Track Eel M. favus, which is smaller reaching only 26 inches (70 cm) in length. These two are often confused as juveniles because they are so similar looking. But despite their very similar appearances, there are recognizable differences. Overall their coloration is quite similar and they both have a series of irregular dark markings along the entire length of its body. But on this eel, the Zig Zag Eel M. armatus, these markings are strongest on the upper two thirds with the belly portion mostly plain. On this eel, the Track Eel M. favus, they are more extreme irregular markings reaching from the top of its back down through its belly.
- Size of fish – inches: 35.4 inches (89.99 cm) – This fish should not be confused with its very similar looking relative the Track Eel M. favus which is smaller, reaching only 26 inches (70 cm) in length.
- Lifespan: 18 years – Spiny eels have a lifespan of 8-18 years.
Fish Keeping Difficulty
Eels are generally suggested for an aquarist with some experience rather than the beginner fish keeper. Zig Zag Eels are sensitive to being moved around, it is best to purchase a specimen that has been at the fish store for at least a week or else the accumulated stress or two moves will leave this fish very week. Once introduced to its new aquarium it usually takes awhile for it to get over its shyness. The first few weeks can be extremely difficult getting them to eat.
They do require extremely pristine water. They have very small scales protecting their body so are prone to fungus and parasites and very sensitive to medications. These fish respond poorly to copper based medications, so these should be avoided. If cared for properly, these eels get fairly large and can live for a long time.
- Aquarium Hardiness: Moderately Difficult
- Aquarist Experience Level: Intermediate
Foods and Feeding
In nature these fish are omnivorous. They feed at night on benthic insect larvae, worms, and other aquatic invertebrates, but they will also eat some plant matter. Like all spiny eels they prefer a diet of live and fresh frozen foods such as brine shrimp, black worms, earthworms or bloodworms.
Some Zig Zag Eels can be trained to eat freeze dried brine shrimp or bloodworms but this is not something that can be counted on. They will also eat small fishes so make sure their tank mates are too large to be able to fit into their mouths. Even half grown specimens can make a quick snack out of small goldfish and livebearers like platies without much trouble.
Eels only need to be fed a couple of times a week and some may refuse food offered more than that, then often eating only once every two or three weeks. These eels are normally nocturnal feeders so make sure they are getting their share of the food. The middle and top inhabitants will often eat all the food before it sinks.
- Diet Type: Omnivore
- Flake Food: No
- Tablet / Pellet: Occasionally – Not all specimens will accept processed foods.
- Live foods (fishes, shrimps, worms): Some of Diet
- Vegetable Food: Some of Diet – Some Zig Zag Eels will accept vegetable matter, but this is fairly rare.
- Meaty Food: Most of Diet
- Feeding Frequency: Weekly – Eels only need to be fed a couple of times a week, and sometimes will eat even less.
The most important thing for these eels is that they always have clean and well-oxygenated water. Frequent water changes of about 30% a week are needed for this eel. With your weekly water change make sure to vacuum the gravel to remove all excess food and waster. but It’s best not to remove any bio film on rocks and decor. A magnet algae cleaner normally does a great job in keeping the viewing pane clear.
It is also helps to add efficient bottom cleaning tank mates to keep the bottom free from decaying foods in between cleanings. Be careful however, to add bottom cleaners after your eel is adjusted to its tank and is eating.
- Water Changes: Weekly – Water changes of about 30% weekly.
Zig Zag Eels will spend most of their time on the bottom of the aquarium. This species of spiny eel can eventually grow to be quite large so plan accordingly. That cute little 4 inch fish may eventually grow to over 2 feet long! Keep small specimens up to 6 inches in a tank that is at least 36 inches long and about 35 gallons. Larger specimens will needing an even bigger area, tanks that are 48 inches in length or longer and 55 gallons up to 100 gallons will be necessary as they grow.
They do best in a soft to medium water with good water movement that provides plenty of oxygenation. These fish require pristine water. The tank water should turnover at least 10-15 times per hour. An undergravel filter is a great choice for these fish as it creates high oxygen through out the tank as well as reducing the waste. A canister filter or powerheads and airstones can be introduced to achieve proper flow and oxygenation. This fish will also devise many creative escape attempts if given the opportunity, therefore the aquarium should have a tightly fitted hood.
They like a dimly lit aquarium or one with floating plants to help subdue the light. If their tank has a sand or fine gravel substrate, they may burrow into it. Make sure they have plenty of hiding places so they will feel secure in their new home. Provide other decor such as rocks, caves, and roots to give it some dark areas to retreat. PCV tubing also makes great caves for these long eels. Be sure to place heavy decor firmly on the bottom. These fish are not actively destructive, but because of their size and burrowing nature, they can dislodge anything that gets in their way, including plants. Multiple hiding places need to be made for the eel to feel safe in the tank.
These eels are primarily freshwater eels in the wild, but they can tolerate slightly brackish conditions. For their long term health however, the specific gravity should be kept at 1.005 or less. They are not suited for the types of brackish aquariums that the truly brackish water fish, like Mono’s and Scats, do well in.
- Minimum Tank Size: 100 gal (379 L) – This fish needs a tank long enough for it to stretch out in. Juveniles will be fine started in about 35 gallons, but 100 gallons is the minimum size needed for an adult.
- Suitable for Nano Tank: No
- Substrate Type: Sand/Gravel Mix – Provide a sand or fine gravel substrate so they can burrow.
- Lighting Needs: Low – subdued lighting – In moderately lit tanks, provide floating plants to help subdue the light.
- Temperature: 72.0 to 82.0° F (22.2 to 27.8° C)
- Range ph: 6.5-7.5
- Hardness Range: 5 – 15 dGH
- Brackish: Sometimes – Primarily freshwater fish, but they can tolerate slightly brackish conditions.
- Water Movement: Moderate
- Water Region: Bottom – Zig Zag Eels will spend most of their time on the bottom of the aquarium.
They are a nocturnal species but are generally peaceful and shy. They mostly ignore other tank mates although they may eat fish that are small enough to fit into their mouths. Some species of spiny eels can get territorial and aggressive with their own kind. A general rule of thumb is to keep them singly unless you plan to breed. Also their large size as adults makes it difficult to keep more than one in an aquarium. It takes a very large tank with many hiding areas to keep multiple specimens.
- Venomous: No
- Temperament: Semi-aggressive – This fish is generally shy although it will be highly aggressive with its own kind and is for this reason generally kept singly.
- Compatible with:
- Same species – conspecifics: Sometimes – Only keep more than one if you intend to breed, or if the tank is very large with enough room for each eel to have undisturbed territories.
- Peaceful fish (): Monitor – Tank mates need to be large enough to not be eaten.
- Semi-Aggressive (): Monitor
- Aggressive (): Monitor
- Large Semi-Aggressive (): Monitor
- Large Aggressive, Predatory (): Monitor
- Shrimps, Crabs, Snails: May be aggressive
- Plants: Monitor – hese eels will uproot most planted plants.
Sex: Sexual differences
Sexual differences are unknown and it is almost impossible to identify the sexes, though a mature female may be more full bodied.
Breeding / Reproduction
The Zig Zag Eel has not been bred in captivity. Only a few spiny eels have been bred in the aquarium, possibly because they are generally kept singly rather than in a group where a male and female can find each other. Though it is not documented what makes them spawn, trying to emulate the bounty of the flood season can help stimulate breeding behavior. Feed more and higher quality food than you normally would and providing an influx of clean water. Their courtship lasts for several hours, where they chase each other and swim in circles.
The eggs are deposited among floating plants. They are sticky so will adhere to the plants and then hatch in 3 to 4 days. The fry becoming free swimming a few more days after that and should be fed nauplii. The fry are something of a challenge to raise as they are susceptible to fungal infections. Regular water changes and the use of an antifungal water treatment can help.
- Ease of Breeding: Unknown – This fish has not been bred in the home aquarium, however it is presumed that their breeding process is similar to other Spiny Eels.
Eels are prone to diseases caused by parasites and fungus, so take caution when introducing these fish to an established tank. Eels are also very sensitive to medications used to treat many diseases; a separate hospital tank is needed. Very low water temperatures and condition changes can also cause stress to this fish which makes them even more prone to disease. Take great care when netting eels as they have very delicate and scraps can make them even more prone to disease.
The most common disease that an eel is susceptible to is Ich. Ich is short for Ichthyophthirius, also known as “white spot disease”. It is a parasite that can attack nearly all aquarium fishes, but you’ll find that Eels are often the first to be attacked. Take great care in treating ick as eels are very sensitive to the medications used to treat it. Often the dose is half of what is normally used. If nervous or unsure about medications, use Reef safe medications.
An outbreak of disease can often be limited to just one or a few fishes if you deal with it at an early stage. When keeping these sensitive types of fish, it is common to catch deteriorating water conditions and disease before other fish are affected. The best way to proactively prevent disease is to give your Zig Zag Eel the proper environment and give them a well balanced diet. The closer to their natural habitat the less stress the fish will have, making them healthier and happy. A stressed fish will is more likely to acquire disease.
Anything you add to your tank can bring disease to your tank. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so not to upset the balance. It is recommended to read up on the common tank diseases. Knowing the signs and catching and treating them early makes a huge difference. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.
The Zig Zag Eel M. armatus is commonly available and reasonably priced. Be aware when purchasing as this eel is often misidentified as the Tire Track Eel M. favus. These two similar looking eels attain a much different adult size it is important to know which eel you are purchasing. The Zig Zag Eel can grow to about 36″ in length while the Tire Track Eel can reach up to 28″.
- Animal-World References: Freshwater Fish and Plants
- Dr. Rüdiger Riehl and Hans A. Baensch, Aquarium Atlas Vol. 1, Publisher Hans A. Baensch, 1991
- Joseph S. Nelson, Fishes of the World, Wiley, 2006.
- Neale Monks, Brackish Water Fishes: An Aquarist’s Guide to Identification, Care & Husbandry, TFH Publications, 2006
- Dr. Herbert R. Axelrod, Aquarium Fishes of the World, TFH Publications, 1998
- Dr. Herbert R. Axelrod, Dr. Warren E Burgess, Dr. Cliff W. Emmens, Neal Pronek, Jerry G. Walls, Ray Hunziker, Dr. Axelrod’s Mini-Atlas of Aquarium Fishes, Mini- Edition, T.F.H. Publications, Inc., 1987
- Mastacembelus armatus (Lacepède, 1800) Zig-zag eel, Fishbase.org
- Mastacembelus armatus, The IUCN Red List of Threatened Species
- Tire track eel, Wikipedia, The Free Encycopedia