By thus time it was clear that the punishment of the mild electric shock was causing an association to be established. The association made by the fishes at this time was definite and distinct but not at all of the nature anticipated. At this time the reaction was for either or both fish to rush at the other and to bite at its fellow. These fish lack jaw teeth and are evidently unable to inflict any considerable injury. They can exhaust one another, however, by such attacks. Thus by the time about fifty shocks had been administered, one of the fish was rather badly beaten and doubtless would have died if the experiment had been continued.Besides being rather cruel, I thought it was hilarious that the side effect of the shocks would turn the fish against each other instead of making them swim together. Turns out the fish assumed the other fish was the one causing the shocks, hence the attacks.
Breder, C.M., Jr., & Halpern, F., 1946, Innate and Acquired Behavior Affecting the Aggregation of Fishes: Physiological Zoology, v. 19, p. 154-190.
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