When Is A Dolphin Not A Dolphin?

One of the coolest, and most intelligent oddball fish you can keep in an aquarium is Mormyrus longirostris. They have a few common names. Most often you'll see them called “Eastern Bottlenose” and less frequently “Elephant Snout” which is a name better suited to another fish in the genus. You'll also frequently see them called “Freshwater Dolphin.” While this is a testament to their intelligence, a topic we'll revisit later, they're not actually dolphins (or even mammals), they're fish.

Mormyrus longirostris is a very unique looking fish with a body coloration and eyes not unlike the Dolphin they're inaccurately named after, but with a down turned fleshy nose like the beginning of a trunk. While this is odd, what is most interesting about these fish is their uncanny smarts. Eastern Bottlenose will quickly recognize their handlers and can distinguish between people. They can recognize patterns and solve simple puzzles that befuddle most fish that many aquarists deem “smart.” Some Eastern Bottlenose owners even report being able to teach their fish tricks!

As a result of this intelligence, these fish will do best when given some enrichment in their tanks. People often offer them small sinking balls and rings to play with in their aquariums and the internet abounds with videos of these fish moving these items around and swimming through hoops. The next thing to consider about their tanks is that the display is going to have to be large. Mormyrus longirostris is a fish that grows quickly (up to ½ inch a month) to a quite large adult size. Fishing-worldrecords.com lists the largest, photo documented Eastern Bottlenose as 28 inches long and 15 pounds. The record weight is 22 pounds, and the record length is 33 inches! When this fish hits adulthood, you're going to need a tank that is at least 300 gallons. Flow and lighting should both be fairly sedate.

This substantial size means they are targeted and caught for sport and food all throughout their native range, which is primarily the Zambezi River in Africa, though they are also found in several other rivers in Tanzania, Malawi and Zambia. They are found both singly and in groups. They use electrical organs in their snout to locate food in sand and silt in the slower moving portions of their home rivers. They can hunt in groups, and it is hypothesized that they can communicate with each other with via the same electrical pathways. They live mostly on invertebrates like aquatic insects, worms and clams, but will also eat fish that they can catch and are small enough for them to get down. In regard to feeding them in the home environment, this means they often need to be fed live food initially. Red worms, tubifex and grubs are all good choices for this. We've also had good luck feeding them thawed Gamma Bloodworms and smaller specimens will usually happily take Gamma Mysis. Some individual fish will learn to eat pellets like Nutramar Complete, but many will continue to reject processed foods for some time. Feed your Mormyrus longirostris at least three times a day when small, and this number can slow down a bit once they are mature and can handle larger meals in one feeding.

Husbandry wise, Eastern Bottlenose are the tale of two fishes. When they are small, wild specimens are frequently shy, docile and very susceptible to shifts in water quality. Aquacultured specimens have been shown to be much hardier much earlier in their lives. Once they are about five or six inches long and acclimated, they are extremely hardy, outgoing and can become somewhat aggressive. This aggression comes with an asterisk in that Mormyrus longirostris doesn't have any teeth and so does little or no damage to the fish it pushes around. As a result, they are often kept as a single fish and are surely cool and engaging enough to pull this off, but they can also be housed with other large fish like Oscars, Datnoids, many larger Catfish / Plecos and Peacock Bass to name a few. Avoid fish that are super aggressive and could beat up the Bottlenose, as they do not see well and can get bullied too. Even though they heal very quickly, they will become reclusive if picked on constantly. The electrical organs of the Eastern Bottlenose can be affected by other “electrical” fish like eels, so do not house them in the same aquarium. Also avoid small fish that might end up becoming a meal.

All of us here love an oddball fish, and a monster oddball is even cooler if you have the space to keep one. Of all the fish we frequently see, the Eastern Bottlenose is possibly the most unique combination of interesting looks and incredible intelligence. If you're looking for the smartest fish around, maybe look into keeping Mormyrus longirostris. Ask your Local Fish Store about getting you a sustainably sourced specimen from us here at Aquatropic!