The Bodhisatta was once a fish. He was the leader of a large school and one time they came upon a crane sitting peacefully, wings outstretched, on the edge of a pond. The fish were impressed by the crane’s demeanor and assumed it was a pious bird. But the Bodhisatta told them cranes are tricksters and it was really trying to lure them in close enough to catch and eat them. So the fish all splashed in the water and drove the crane away.
In the Lifetime of the Buddha
The crane was an earlier birth of one of the Buddha’s disciples who had been exposed as a hypocrite. The Buddha told this story so the other disciples knew he had been the same way in the past.