When Is An Eel Not An Eel? When It's Spiny!

The Blue Lesser Spiny Eel has dozens of names around the world, but in North America, it has only a couple; it is sometimes (albeit rarely) also known as the Eyespot Eel and the Bengal Eel. This is likely because until very recently, it was relatively rare in the aquarium world here, but more popular abroad. As in interesting aside, all of the “spiny eels” aren't eels at all, as true eels don't have spines in their fins. This being said, Macrognathus aculeatus looks like an eel and behaves like one too, so if a freshwater eel is on your must have fish list, the Blue Lesser Spiny warrants a look!

Macrognathus aculeatus has a wide range in eastern Asia. While it is most commonly found in Borneo, it has also been less frequently found in Java, Sumatra, Myanmar, Thailand, Vietnam and China. Larger adults frequent medium and large rivers, while juvenile specimens are more likely to be collected from wetland areas. They get about ten inches long or so, though the record length for a specimen is just under 15 inches! They develop into a gorgeous cobalt color with golden fringes and tail spots along the top of their tail end.

Contrary to popular opinion, none of the commonly available spiny Eels need brackish water; they all live and breed in freshwater and the Blue Lesser Spiny is no exception; they prefer water that is on the soft end of the spectrum that is slightly acidic (pH 6.5 to 7 or so). Normal tropical temperatures should be your goal, think 72-80 Fahrenheit.

As they can get pretty large for aquarium fish, we recommend a 75-gallon tank as a minimum size. They will not need this full volume or depth, but this 48” length and 18” width gives them a good footprint to explore. Obviously, larger is never going to be a problem. Small specimens could be kept in a tank as small as a 40-gallon breeder but be aware that they will outgrow this tank in time. Like all the fish that we call freshwater eels, a cover for this tank will be required as they are notorious escape artists, which usually has disastrous results. Flow should be gentle, so this needs to be balanced with the need to get them adequate filtration. We suggest having a filter that will turn the aquarium over five to ten times per hour.

While, Macrognathus aculeatus is usually found in areas with a lot of plants, you'll need to be selective in the plants you choose if you want to go this route with your display. They like to dig and make burrows and while they won't consume any plant material, they are pretty likely to dig them up. They prefer somewhat dim conditions, so floating plants that give them some shades are a great choice. You could also use plants that are attached to décor like Java Fern and Moss or Anubias species. As burrowers, they are going to do best in displays that have some sand, an inch or two is plenty. Avoid course gravel substrates as they can damage themselves in it. They do well with all sorts of driftwood and smooth rocks and will appreciate the cover. Some aquarists also give them PVC tubes to hide in. Place all heavy décor directly on the aquarium bottom, rather than on the sand to prevent the Spinies from collapsing the rocks as they dig around.

Macrognathus eels are good eaters, though some can be picky to feed initially. They are shy and generally nocturnal and so in the beginning, some individuals may need to be fed live food at night. They are opportunistic carnivores and will relish earthworms, a natural food for them that they respond well to, are easy to buy and dose and generally fun for aquarists to feed. They will also relish feeder guppies, ghost shrimp, bloodworms etc. Small specimens will happily take tubifex, mysis and brine. In time, you can train your spiny eels to eat during the day and to take thawed foods. Keeping Blue Lesser Spiny Eels with other fish will make them bolder but be warned that they are opportunistic predators and will eat any fish they can catch and fit in their mouths. Also, because the eels can be tricky to feed, keeping them with other fish can complicate getting food to the eels. If you decide to keep them with other fish, lean toward peaceful, larger fish. Macrognathus eels are rarely bred in captivity and if you're up for it, this would be an excellent challenge. For those you interested in keeping multiples, we suggest a very large aquarium, 180 gallons or more, at least six feet in length and two feet wide as a starting point to reduce aggression. They are hard to sex even as adults, though females will be “thicker” than their male counterparts. Successful attempts at breeding other Macrognathus species in the past has been triggered by heavy feeding and large regular water changes. Hundreds, even up to a thousand or so, sticky eggs will be deposited on just about anything plant based. These eggs are fairly large (over 1mm) and take a few days to hatch. Baby Peacock eels will need really small food like cyclops nauplii etc and this will be a primary challenge for you.

If you're looking for wow factor in your aquarium, Lesser Blue Spiny Eels will fit that bill nicely. They have a reasonable adult size and are hardy as long as they get enough food and have an environment where they can't get scratched as they are prone to infection when wounded. They eat well once established and are tolerant of other fish that are too big to eat. Just take some time to get them acclimated to feeding, keep a tight lid and soft substrate at you're on your way to success! Head over to your LFS and ask them about getting you some Macrognathus aculeatus from Aquatropic today!