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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

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

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)

(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)

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)

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.

Mormyrops anguilloides

Mormyrops anguilloides

The Mountains of Antarctica as seen from the Southern Ocean

The great Southern Ocean which swirls in a clockwise circle around Antarctica is home to many of the Earth’s largest animals.  Blue whales come here to gorge on vast schools of krill. Among the icebergs and the towering waves, southern elephant seals (the largest member of the order Carnivora) fight duels to build their harems, and highly intelligent killer whales hunt together in pods.  There are populations of sperm whales living in the Southern ocean as well and these leviathans dive to the cold floor of the world hunting for the world’s largest mollusk, a huge cephalopod which can only be found in the Southern Ocean.  In fact this bizarre creature, the colossal squid (Mesonychoteuthis hamiltoni) is also the world’s largest invertebrate.  Also known as the Antarctic squid or the giant cranch squid, the colossal squid lives in the abyssal depths.  Unlike other squid, the colossal squid does not have tentacles–its powerful arms are studded with sharp hooks (much like the long-extinct belemnites).  Some of these hooks swivel while others have three barbs in the manner of a fish spear.

The Colossal Squid (Mesonychoteuthis hamiltoni)

The measurements of the colossal squid are staggering.  Its eye alone (the largest of any known creature) measures 27 centimetres (11 in).  A fully grown adult squid is estimated to be 12–15 metres (39–49ft) long.  Although giant squid have longer tentacles, the colossal squid a long stout mantles and are thus much more massive. Their upper weight limits are unknown but are well over 500 kg (+1000 lbs).

The colossal squid is believed to be an ambush predator, which lurks in the depths waiting for chaetognatha, other squid, and benthic fish (such as the Patagonian toothfish) to pounce upon.  It is hypothesized that they have a slow metabolism and do no need great reserves of food (unlike the energetic endothermic sperm whales which prey on them).  The colossal squid are believed to be sexually dimorphic—the females become much larger than the males.

A rare specimen of colossal squid

There is a reason that so much of this article is couched in ambivalent language such as “estimated”, “believed” and “probably”:  colossal squid live in an environment where humankind can barely venture.  The colossal squid are fast enough and clever enough to usually evade our nets, lines, and traps (although fishermen trying to catch Patagonian toothfish hooked a 450 kg (990 lb) specimen which was about 39 feet (13 m) long).  Additionally our submarines and submersible robots are too slow and noticeable too stalk the squid in the abyssal depths.  Other ocean creatures do not suffer from the same problem.  Juvenile colossal squid are eaten by beaked whales, elephant seals, sharks, toothfish, and even albatrosses, however the adult squid are so large that only massive sleeper sharks and giant sperm whales can threaten them.  Sperm whales are often covered with scars from their battles with the giants but the whales easily have the upper hand.  Sperm whale stomachs have been found filled with hooks and beaks (which coincidentally were much larger than those found on the largest squid specimens recovered by humans to date).

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