By Peter A. Dill
Animal Behaviour, Volume 25, Part 1, February 1977, Pages 116-121, ISSN 0003-3472, DOI: 10.1016/0003-3472(77)90073-2.

The development of behaviour in Atlantic salmon (Salmo salar) and rainbow trout (S. gairdneri) in a gravel-free environment was observed from hatching to the age corresponding to 1 week after emergence at 15 [degree sign]C (40 days). Records included changes in posture and spatial distribution and the development of swimming, surfacing, ingestive and agonistic behaviour acts. Young fish of both species with large yolk sacs held a posture and locomoted with their head down, had difficulty in remaining upright, and were essentially photonegative. As the yolk sac was exhausted the body axis became more horizontal, an upright position was maintained, and photonegativity was reduced. Surfacing behaviour occurred just prior to the emergence of conspecifics from gravel. Until the age of emergence, the behaviour of the two species was very similar. Upon emergence, rainbow trout became pelagic and exhibited immediate feeding and extensive agonistic behaviour. Atlantic salmon remained on the substrate after emergence, began to feed at the same age as trout but exhibited less agonistic behaviour.

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