Effects of photoperiods on the behaviour patterns of juvenile Atlantic salmon (Salmo solar L.)

Pinhorn, A. T. (1961) Effects of photoperiods on the behaviour patterns of juvenile Atlantic salmon (Salmo solar L.). Masters thesis, Memorial University of Newfoundland.

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Abstract

The behaviour patterns of Juvenile Atlantic salmon exposed to photoperiods (light-exposed fish) and of those exposed to control conditions (control fish) were compared. A negative phototaxis was exhibited by both control and light-exposed fish. The intensity of the light stimulus had very little effect on the intensity of the phototaxis in the light-exposed fish, while the control fish showed an increase in the intensity of the phototaxis with an increase in the intensity of the light stimulus. The control fish showed an increase in the reaction to the light stimulus the longer the stimulus was applied at the higher levels of stimulation, while the light-exposed fish exhibited this behaviour at the lower levels of stimulation. Both the control and light-exposed fish preferred currents to still water, but the preference of the light-exposed fish was stronger than that of the control fish. The control fish tended to avoid the faster flowing water to a greater extent than the light-exposed fish, while the latter were more sensitive to changes in current intensity. In a vertical light gradient, the light-exposed fish were very active, moving rapidly up and down the water column, while the control fish were relatively quiescent and settled to the bottom at low light intensities. In a horizontal light gradient, the control and light-exposed fish remained in the areas of low light intensities. Both groups showed a stronger avoidance of the light sources of higher Intensities, but tended to move into the brighter areas with low light sources. The control fish exhibited a stronger reaction to the less intense light gradients than the light-exposed fish, whereas the latter showed the stronger avoidance reaction to the more Intense light sources. These differences in behaviour are attributed to the increased activity and sensitivity of the light-exposed fish, resulting from their exposure to photoperiods. It is shown that the control fish behaved similarly to the salmon parr, while the light-exposed fish behaved similarly to the migrating salmon smolts. The significance of the behaviour patterns studied is discussed in relation to the downstream migration of Atlantic salmon.

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