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Welcome to the world of topsy turvy! When it is a few weeks old, the upside-down catfish (Synodontis nigriventris) turns on its back and spends most of the remainder of life swimming upside down. Indigenous to the Congo basin, the friendly little catfish likes to spend its days clinging to the bottom of submerged logs and rocks. Occasionally it swims along below the surface of the water to hunt for insects. Evolution has already reversed the color scheme of the upside-down catfish: unlike most aquatic animals, its belly is darker than its back. This coloration provides the upside-down catfish with camouflage both from predators/prey looking up at a bright background and those looking down who see a dark background. Like the coral reef catfish, the upside down catfish is more comfortable with others of its kind as seen in the picture below.
The upside down catfish is well known for being a friendly and playful inhabitant of the tropical community tank, however, like most of us, it has a sinister relative. The cuckoo catfish (Synodontis multipunctatus) hails from Lake Tanganyika, an African rift lake filled with mouthbrooding African cichlids. Such cichlids protect their eggs–and later their fry– inside their mouths until the baby cichlids are big enough to fend for themselves.
But the cuckoo catfish have found a way to sabotage the process for their own ends: the female cuckoo cat carefully watches breeding Haplochromis cichlids and zips in to lay her fertilized eggs at the same time the cichlid lays her own. The unfortunate cichlid takes both types of eggs into her mouth. The cuckoo catfish eggs are first to hatch–whereupon the hatchling catfish eat the cichlid eggs. Afterwards the young catfish enjoy protection from the aggressive cichlid parents until they are old enough to fend for themselves.
Over 120 Synodontis species are known to science–which means this particular genus of catfishes accounts for nearly a quarter of the catfish species of Africa. Many Synodontis catfish are colloquially known as “squeakers” due to their habit of making vibrating sounds by means of their pectoral fin spines when handled or disturbed.