Clever Fish in the Deep River (Concerning Elephant Fish)

The Congo River is the world’s second largest river by volume of water discharged (which seems like the most worthwhile measure of a river). Portions of its watershed are both north and south of the equator—which ensures that some part will always be experiencing a rainy season. The Congo River flows through the world’s second largest rainforest, and, as you would expect, the waterway teems with exquisite animals of multitudinous variety. There are aquatic mammals, many different sorts of crocodilians, turtles, frogs, snakes, mollusks, insects, crustaceans, and there are fish fish fish! The piscine variety is staggering: stingrays, carp, cichlids, pufferfish, African tetras, and the highly predatory giant tigerfish. There are also some bizarre blind deep water fish—because the Congo is the world’s deepest river (with depths of at least 220 m (720 ft)).

A few Congo River Fish

Ferrebeekeeper has always been devoted to catfish which thrive everywhere other than the deep ocean or the arctic. Indeed there are all sorts of catfish in the Congo River—particularly squeakers (AKA upside-down catfish). However, as a special treat, let’s take a break from catfish and talk about an entirely different fish—the freshwater elephant fish (the Mormyridae family from the order Osteoglossiformes). According to the World Wildlife Fund, Elephant fish are the dominant fish fauna in the Congo River. And they are downright strange in so many ways.

Campylomormyrus rhynchophorus

As you might surmise, elephant fishes earned their common name from their long trunk-like mouths (although this feature is certainly not universal among the 200 plus different varieties). Different species vary greatly in size: the smallest elephant fish are only 5 cm (2 inch) when they reach adulthood whereas the largest grow to 1.9 meters (4.5 feet) in length. Like the electrical catfish and ghost knife fish of the Amazon, the elephant fish have electroreceptive sensory organs. These generate an electrical field and “read” the field so the fish can sense the world (and especially other living things) very clearly even in the murkiest waters and in complete darkness.

(Image: Carl Hopkin)

Elephant fish are extremely intelligent fish with a greatly enlarged cerebellum. In fact the fish have a brain body ratio which is approximately the same as humans (although it seems that they use much of their mental power to operate their electrical sensory organs and interpret the electrical data). In humans, the cerebellum controls movement, motor control, and language so it is speculated that elephant fish may have greater abilities to communicate with each other than we currently understand.

Campylomormyrus alces (from aquaria2.ru)

Oh, also the elephant fish (and their closest relatives the African knife fish) are unique in that their sperm lack flagellums. Of all vertebrates—from turkey to megabat to axolotl–these strange African fish are the only chordates not to have motile sperm. I wish I could tell you more about that business, but I cannot (and researching it on Google has not made me happier or wiser).

Genyomyrus donnyi (George Albert Boulenger)

I have tried to show some elephant fish which are endemic to the Congo River, but, alas, I am not an ichthyologist (although that might have been a good career choice) so I may have messed up. Hopefully these photos at least provide some small overview of this incredible family. Humankind needs to learn more about these splendid clever African fish which are so prevalent in the turbid waters of the great tropical river.