Effects of partial ablation of the cerebellum on sustained swimming in goldfish.

To investigate the role of the corpus cerebelli in the control of sustained swimming or cruising in goldfish, Carassius auratus, we conducted experiments examining the effects of partial ablation of the corpus cerebelli (CC) on swimming performance against constant water flow at various speeds. Ten out of 15 CC-ablated fish successfully maintained sustained swimming against water flow even at the highest speed tested (3.0 body lengths per second). This result showed that the CC is not crucial for generating the simple swimming motor pattern, although some effects of the surgical operation itself on the capability of the sustained swimming were found in both sham-operated and CC-ablated fish. However, we found that both tail-beat amplitude and frequency in CC-ablated goldfish tended to be greater than that of control fish at the same swimming speeds. The thrust index (square of the value obtained by multiplying the tail beat frequency (Hz) by twice the tail beat amplitude (mm)) was significantly larger in CC-ablated fish than in control fish at higher swimming speeds (> or =2.0 body length per second). This result suggests that CC-ablated goldfish produced more thrust by tail beats than control fish to maintain sustained swimming at higher speeds. We concluded that in goldfish the CC plays no major role in the posture control and generation of simple forward swimming movement, although the integrity of the CC is important for execution of normal swim gait.