By D.W.M. Herbert
Animal Behaviour, Volume 11, Issues 2-3, April-July 1963, Pages 347-350, ISSN 0003-3472, DOI: 10.1016/S0003-3472(63)80123-2.

1. One-year-old rainbow trout of an autumn spawning strain which had been kept swimming for several months against a circulr current of water were observed to reverse the direction in which they swam when the current was stopped. The majority would continue swimming circuits of the aquarium in the new direction for more than 5 hours. Yearling rainbow trout kept swimming against the current from January, did not reverse their direction until the end of April, and the development of this behaviour coincided with the loss of parr marks and the assumption of adult markings.
2. Brown trout parr from an upland stream did not reverse their swimming direction when the circular current was stopped.
3. For several weeks after the reversing behaviour had developed, the sign of the response could be changed by submitting fish for about two days to a circular current flowing in the opposite direction, but at a later stage the direction taken by the fish when the current stopped appeared to become fixed.
4. Reversal did not occur if the current was stopped when the aquarium was in total darkness, nor unless the fish had been able to see their surroundings for approximately 2 to 3 hours after a period of 1/2 hour in total darkness. Well established swimming in the reversed direction through still water was abolished by 5 minutes in total darkness.

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