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The Mochokidae are a family of African catfishes known commonly as ‘squeakers’ and ‘upside-down catfishes.’ These common names refer to some unusual habits of certain members of the large genus Synodontis. The name squeaker refers to the fact that, when agitated, many species in the genus are capable of making a squeaking noise by stridulation of the pectoral spine against the pectoral girdle (Jubb, 1967); stridulation is also apparent inMochokiella paynei and some species of Atopochilus.
Even more peculiar is the habit of some species of Synodontis that are known to swim upside-down. This habit seems to be correlated with feeding while upside-down at the water’s surface (Bishai & Abu Gideiri, 1965b), but upside-down catfishes will rest and swim in the inverted position on a regular basis. Chapman et al. (1994) showed that an upside-down posture near the surface also facilitates respiration in poorly oxygenated water. While the genus Synodontis presents the most well-known species with their fascinating behaviors and natural histories, the family is actually much more interesting when taken as a whole.
Mochokid catfishes are currently restricted to the freshwaters of Africa, but are nearly ubiquitous in the habitable waters of the continent. A high degree of morphological diversity allows mochokid catfishes to inhabit some of the fastest flowing streams and cataracts to the widest and deepest stretches of the Congo River. Mochokids also inhabit the massive African rift lakes like Tanganyika, Victoria and Nyasa. The greatest diversity of mochokids almost certainly occurs in the Congo River and its numerous tributaries, but they are also found in many of the rivers and lakes of western Africa, southern Africa, eastern Africa and in the Nile. Like a handful of other catfishes, some mochokids are known to swim in mid-water; other members of the family are primarily benthic. Likewise, some mochokids shoal while others are rather solitary. As a rule they are most active during the night, but they can be found hiding amongst plants, logs and other submerged structure during the day.