by Marco Lichtenberger

 

Among the oddball fishes frequently seen in the hobby is a family known as the Spiny Eels. At first glance, they may appear like a cross-breed between an anteater and a snake! Spiny Eels are distributed in Africa, as well as in Southern and Eastern Asia. In contrast to many other eel-like fishes, which are not closely related to them, they have pectoral fins that are often constantly moving like a rotor of a helicopter. Especially their dart-like movement, their ability to stop suddenly, and their habit of burying themselves in the substrate until only their expectant eyes and strange trunk-like snouts are visible, make them adorable pets. However, they have a bunch of specific requirements that need to be known in order to keep them successfully for many years.

 

Species 

The common name “Spiny Eels” comes from the spines found along their back. They are not closely related to the true eels, but share a similar life style and thus comparable appearance. There is quite a number of Asian spiny eels in trade regularly. The designation of the different species to the most common genera Mastacembelus and Macrognathus is not always handled uniformly. It is best to employ the species names for a first orientation. The nomenclature used in this text is following the recent FishBase version of 2007. It is not uncommon at all that the labels in the fish stores are wrong. Nonetheless, it important to know which species you are actually buying. Although care is similar for all of them, their maximum size varies drastically. A number of smaller species usually will attain something around 20 cm (8 inches), while bruisers such as the "Zig-Zag Eel, Mastacembelus armatus will reach 90 cm (35 inches) and consequently need large tanks. A good indication on how large your future Spiny Eel will get is its caudal (tail fin). The smaller Asian species (at least the ones commonly traded) have a caudal fin separated from their dorsal and anal fins, while the larger species have a continuous fin running around the end of the body not unlike Moray Eel

Related to the popularity of African cichlids, the increase of African spiny eels in the aquatic trade (e.g. Mastacembelus loennbergii), which share the habitats of the cichlids, adds to the Spiny Eel confusion, because they do not seem to obey the separate tail fin rule of their Asian relatives. For the African species the genera Aethiomastacembelus, Afromastacembelus and Caecomastacembelus have been employed. Asking in the shop for the origin of the eels thus may be useful, although it can be discussed how reliably such information is. It always is a good idea to search the entire Mastacembelidae (family of spiny eels) at www.fishbase.org to get familiar with the typical coloration and markings of the common species, instead of buying some spiny eels that will get larger than the tank you thought they should live in.

Big species frequently seen in trade are the Fire Eel, Mastacembelus erythrotaenia, the Tire Track Eel, Mastacembelus favus and the Zig-Zag Eel, Mastacembelus armatus. Among the smaller species you may be able to get your hands on are Macrognathus aral, the Peacock Eel, Macrognathus siamensis and the Zebra Spiny Eel, Macrognathus zebrinus. Another regularly-traded small species is Macrognathus pancalus, often not recognized or confused with juvenile Mastacembelus armatus and other species.

Macrognathus pancalus has numerous common names such as "Striped Spiny Eel", "Barred Spiny Eel", "Zig-Zag Eel" (just like M. armatus), "Yellow Fin Spiny Eel", "Indian Spiny Eel" and others. The typical coloration can be observed on the pictures of this article. The overall darkness of the fish and the actual amount of yellow in the coloration is variable, though.

The species is common in India, Pakistan, Bangladesh and Nepal. Aside its importance for the aquarium trade it is a very in-demand and regionally pricey food, although it is a rather small species. The following descriptions of proper husbandry are made for M. pancalus, but they may be extended carefully to other small Asian Spiny Eels.

[pancalus00.jpg]                       [pancalus04.jpg]

 

Water Parameters 

In nature M. pancalus occur in a wide range of water types. They are abundant in flooded rice fields as well as in slow moving rivers and even brackish water estuaries. Long-term husbandry experience confirms they can be successfully kept in hard freshwater as well as in low (specific gravity approx. 1.005) to medium (specific gravity approx. 1.010) brackish water. Higher salinities are probably disliked and may result in increased jumping.

A positive effect of brackish water seems to be that skin abrasions, which the Spiny Eels regularly can get when trying to slip through narrow rock gaps, do not infect and seem to heal faster than they do in soft acidic water, in which fungus or bacterial infections may occur. Although no white spot infection of M. pancalus seems reported, saltwater baths should well be possible just in case.

A perfect compromise with regard to their natural biotopes may be to keep them in lower end brackish tanks, but hard fresh water is equally adequate.

M. pancalus accept a pH between 6 and 8, but might do best in neutral to alkaline water. Hard water is favoured above fresh water. Temperature should be between 20 and 27°C (68 - 81 F). As in all fish tanks nitrites and ammonia should be absent and nitrates should constantly be kept low with regular water changes.

 

 

Tank Setup  

M. pancalus attains a total length of 18 cm (7 inches). They should be kept in tanks not smaller than 60 l (15 gallons). If they are supposed to share their tank with a few other inhabitants, a 120 l (30 gallons) tank should be the minimum. If you want to keep more than two, add about 15 gallons per additional Spiny Eel because of their sometimes territorial behaviour.

Barred Spiny Eels are jumpers, as are many of their family members. A lid is needed to prevent the fish from dying outside the tank. Filter inlets and outlets should be secured with mosquito nets.

Spiny eels in general like to bury, only parts of their head and their typical nostrils are sticking out of the substrate. The intensity of this behaviour may be related to their tank mates, though. When first introduced to a new tank, a pair of Barred Spiny Eels buried themselves immediately, but after several days they stopped burying themselves. Since then, they preferred cavities in the aquarium decoration as hiding spots and did not bury for several months. When a new large Fiddler Crab was added to their tank, they seemed to be intimidated by the more or less peaceful crab and started to bury again.

Planting will contribute to the comfort of the Spiny Eels as well as to the water quality of the aquarium. Rooting plants will suffer under the digging activities of the eels. It is possible to employ heavy flower pots perhaps in a mosquito net to prevent the eels from digging inside the pot. In addition, epiphytic plants, such as Java fern or Java moss can be used. Floating plants also seem to be appreciated much by the eels.

The skin of the Spiny Eels is covered with small scales. However, they are prone to skin diseases and infections especially at grazes they achieved during their burying and hiding activities. Spiny Eels do best with sandy substrates. Fine-grained gravel is also adequate if the grains are rounded. Avoid sharp rocks, such as some lava rocks. Some eels will readily accept tank safe tubes buried in the substrate and similar holes that can be created with rocks and other pieces of decoration. Provide enough of these hiding spots to avoid possible fights. When incorporating rocks, be careful not to use rocks with very narrow holes in which the spiny eels can get stuck. Aside starving and jumping out of the tank, it is not uncommon they die this way.

Spiny Eels are predominately nocturnal and can surprise you each morning with their latest ideas on how to change the decoration of the tank. However, in calm tanks they are also often visible during day time. Rarely they are chasing each other, but most of the time they are sitting in their hideouts carefully watching everything around them. Most activity can be observed if a specific feeding time is kept.

 

Feeding 

Most of the dissected stomachs of wild-caught barred Spiny Eels were found empty. That indicates they do not eat regularly in nature, and that feeding them every other day or only once or twice a week may most resemble their feeding habits in their natural habitat. Feeding them daily will help to train them to be active during the day, though. They do not need much food and are easily overfed, resulting in very lazy fat eels!

From aquarium observations, as well as from scientific studies, it seems that M. pancalus are "stenophagic". That means they have a diet consisting of only a few species in contrast to other fishes that eat everything crossing their way. Spiny Eels can be considered picky eaters. In nature insect larvae are reported to be their main food. They are supplemented with annelids (earth worms and similar) and small crustaceans, as well as with small fishes.

In tanks they often only eat live food for several weeks. Readily accepted were live bloodworms, live blackworms, live Tubifex and live earthworms collected from a toxin safe garden. In the long run only frozen earthworms could be added to this diet, although a number of common training methods e.g. not feeding for a week, dangling food on cotton strings and soaking the food in dissolved vitamins were tried for about a year. That is why  I always keep a box of frozen earthworms, just in case live food is not on hand.

Other hobbyists have had more success and were able to feed their Barred Spiny Eels with frozen bloodworms and Tubifex.

Spiny Eels are not forceful enough to compete with very active species for food. Even a few Bumblebee Gobies are capable of eating away most of a tank ration of live bloodworms before their eyes. If spiny eels are kept in a community tank with active fish, it may be a good idea to feed them with tweezers. Earthworms, in this case, are probably the best food for practical reasons. In contrast, feeding live Tubifex or bloodworms with tweezers, while trying to outrun a wild bunch of hungry fish, is a pain in the neck. An advantage of feeding with tweezers is that you can ensure that everyone gets something to eat.

 

Tankmates 

M. pancalus seem to be unable to rip out pieces of meaty food. So, any fish which does not fit into their mouth should be safe. However, they are capable of nipping the fins of other fishes. This bad habit only seems to occur with other Spiny Eels of the same or other species, and may be interpreted as intraspecific aggression or territoriality. Most likely the fin nipping will stop after some weeks, when the territorial skirmishes have been settled. They never do much physical damage anyway and the fins will grow complete again very fast.

Aside livebearer fry, they have not consumed other fish. Anything at least as heavy as a large Bumblebee Gobies (beware there are very small and larger species) is probably safe from the Spiny Eels, which leaves a lot of possible tank mates for freshwater tanks and even a good number of fishes for lower end brackish tanks. However, Spiny Eels should not be kept with aggressive and predatory fish species or fin nippers. The lower-end-brackish Puffer T. biocellatus (figure 8 puffer) seems to be a good tank mate, but some individuals of this species will bother the Spiny Eels with fin nipping for some time. Wrestling Halfbeaks are a group of species commonly available for low-end-brackish tanks, which will not interfere much with the Spiny Eels.

 

Breeding 

Because of the decreasing numbers of M. pancalus in the wild, hobbyists should be encouraged to breed this species. A number of reports on the spawning and rearing of fry, especially of M. pancalus, but also of other species, exists. Unluckily, own experiences in breeding M. pancalus are unavailable, yet.

It is not always easy to tell apart male and female Spiny Eels. Generally, the females are larger, heavier and have a white belly, while the males are smaller, more slender and have a more yellow belly. Females may also exhibit a larger protruding anal tube, called urinogenital papilla, used to lay eggs. All these characters are not foolproof, making it difficult to select male and female specimens at a store.

A most interesting aspect with regard to keeping a number of spiny eels together is that they seem to spawn in groups consisting of one female and several males. Given their natural ratio of males and females is 1:1, it seems the males may participate at several of these group spawnings in nature. During courtship the males direct their snouts towards the gill area of the female.

The female attaches the sticky eggs to floating plants close to the water surface. The eggs have a diameter of about 1 mm, tiny fry hatch after 3 days. The parents do not care for the fry, which should be transferred to a separate tank. They are swimming and drifting in the water column for about one week and then begin their usual benthic mode of life on and in the substrate. Following literature, they can be easily raised with live Artemia, Daphnia and Cyclops. In only 3 weeks they may reach a length of 3 cm and can be fed with Tubifex. 

Final Thoughts 

The Barred Spiny eel, M. pancalus, can be a nice fish for a fresh water or lower-end-brackish community tank. They need a fine-grained substrate and have extravagant feeding preferences, demanding live food or feeding with tweezers in most cases, but they are really amusing oddballs, which will not cause much trouble given proper husbandry.

 

 Literature

Karim M.A., Hossain A. (1972): Studies on the biology of Mastacembelus pancalus (Ham.) in artificial ponds. Part II. Sexual maturity and fecundity.- Bangladesh Journal of Biology and Agricultural Sciences, 1, p. 15-18.

Schoenebeck, K.-J. (1955): Haltung und Zucht von Pfeilschnaebeln.- DATZ (Deutsche Aquarien und Terrarienzeitschrift), 8(1), p. 5-7 (in German).

Serajuddin, M. & R. Ali (2005): Food and feeding habits of striped spiny eel, Macrognathus pancalus (Hamilton).- Indian Journal of Fisheries, 52(1), p. 81-86.

Swarup K., Srivastava S., Das V.K. (1972): Sexual dimorphism in the spiny eel, Mastacembelus pancalus.- Current Science, 41(2), p. 68-69.