The upside-down catfish
Synodontis nigriventris has a unique habit of swimming and resting upside-down in free water. This behavior leads to the assumption that the catfish has a specific gravity information processing system. We examined the postural control behaviors in the catfish under clinorotation which is usually used for producing pseudo-microgravity.
Synodontis nigriventris kept its body posture at a stable area of the rotated flask in which the catfish was kept, when it was clinorotated at the rate of 60 rpm. In contrast to
Synodontis nigriventris, a related species,
Corydoras paleatus, did not show such steady postural control. When the flask was rotated at a lower rate of 30 rpm or a higher rate of 100 rpm,
Synodontis nigriventris as well as
Corydoras paleatus showed a considerable disturbed control of body posture. In this condition, they were frequently rotated with the flask. These findings suggest that
Synodontis nigriventris has a high ability to keep upside-down posture and the gravity sensation in this catfish is likely to contribute to its different postural control from that of many other fishes.
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