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February 27, 2015

Mormyrus longirostris “Dolphin Mormyrid” or “Eastern Bottlenose Mormyrid” is a fish on many people’s wish lists. Despite its large potential size of 30 inches and particular care requirements, its intelligence and personality have earned it a place in many a dream aquarium. Their large size and relative abundance have made them important food fish in their native habitats, as well as sport fish for anglers. The record weight and length of an angled fish was 22 lbs and about 33 inches according to, which is consistent with the maximum size and weight listed on Fishbase. These fish have been found in South African rock paintings, attesting to their historical significance as a food source.


In nature these fish are nocturnal shoalers, found in loose aggregates amongst muddy-bottomed areas with cave-like structures and aquatic plants. They’re true omnivores, feeding opportunistically on weeds, insects and other invertebrates, and fish eggs and fry. Breeding occurs during the rainy season and migrations are intermittent and irregular. Anglers frequently report feeling mild shocks if handling these fish with bare, wet hands – though this is not dangerous. As aquarium occupants, the Dolphin Mormyrid are intelligent and personable fish – they can be trained to perform adorable tricks, as evidenced in the highly amusing video below.

In home aquaria, these are known as somewhat temperamental with tankmates – many people successfully keep these fish in carefully chosen and researched community aquaria, but it is highly advised that, if one is to attempt this, backup housing for possible conflicts is easily attainable. Common reports of compatibility issues tend to revolve around bottom-dwelling fish such as loaches and catfish, though plecos are often left alone.   Most reports of intolerance, however, involve other species of mormyrid and other weakly electrical fish. It is believed by some keepers that the conflicting electrical signals of the various species will irritate each other until one or more of the fish jump from the tank to escape. We’ve found no scholarly articles supporting this. In contrast, there is documentation that this is an expression of territorialism against similarly shaped fish rather than a reaction to another fish’s electrical signals. For example, the closely-related Mormyrus kannume and Gnathonemus petersii are incredibly territorial, solitary fish and will not tolerate conspecific or similarly-shaped tankmates. One will likely have better luck keeping a group of M. longirostris as they are known shoaling fish – given enough space to each establish its territory, they should be tolerant of conspecifics. They should absolutely not be housed with M. kannume, G. petersii, or any other solitary mormyrid species.

If you are considering housing your Dolphin Mormyrid with tankmates, we’d suggest a larger, robust schooling or shoaling fish that stays in the middle to upper levels of the water column. A decent choice could be Puntius lateristriga “Spanner T Barb”. These 5-6 inch fish are brass colored beauties with distinct black banding – Two vertical black stripes run from the middle of the body and the front of the dorsal fin. A thick black band marks the lateral line from the caudal peduncle to the rear of the dorsal fin, and a circular black dot can be found on the ventral edge of the fish, just above the anal fin. The fish’s bodies deepen and darken as they age, giving the adults an egg-shaped profile with a brown to bronze head and shimmering brass-colored dorsal side. These fish are tolerant of quite a variety of water conditions as long as they are kept warm. Be sure to provide a large home for these fish as they are a shoaling species.


Thank you for reading and I look forward to writing for you again next week!

Jessica Supalla