The fish telencephalon seems to be involved in spatial learning and memory in a similar manner to the hippocampus of the land vertebrates. For instance, telencephalon ablated goldfish are impaired in the post-operative retention of a `spatial constancy' task, which requires the use of mapping strategies, but not in a directly cued task in which responses are based in a guidance strategy. In this regard, previous experiments showed that intact goldfish trained in the spatial constancy task presented considerable behavioral flexibility, as they showed fast reversal learning, that is, they required less training compared with animals trained in the directly cued task and made a lower number of errors to master the reversal than in acquisition. The purpose of the present work was to investigate if the goldfish telencephalon is involved in the faster reversal learning of the animals trained in the spatial constancy task. Goldfish with bilateral telencephalic ablation, sham operated or intact, were trained in the spatial constancy task or in the directly cued task. Telencephalic ablation selectively impaired reversal learning in the animals trained in the spatial constancy procedure. Ablated animals in this procedure reversed more slowly than control animals. By contrast, telencephalic ablation did not produce any significant deficit during reversal in the animals trained in the directly cued task. These results provide additional evidence that the fish telencephalon, as the land vertebrate hippocampus, plays a crucial role in the use of flexible spatial representations. (C) 2000 Elsevier Science B.V. All rights reserved.