Increase in Aggression and in Strength of the Social Hierarchy among Juvenile Atlantic Salmon Deprived of Food

• Published in: Journal of the Fisheries Research Board of Canada
• Main Author: Symons, Philip E. K.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1968
• Subjects: Atlantic salmon; Salmo salar
• Online Access: http://dx.doi.org/10.1139/f68-207; http://www.nrcresearchpress.com/doi/pdf/10.1139/f68-207

Aggressive behaviour of Atlantic salmon (Salmo salar) parr, tested in groups of eight, was greater during 3 days of deprivation of food than during 3 days of feeding. Frontal and lateral displaying appeared to increase more than charging and nipping. Increased agression was only partly a result of increased locomotion, and therefore was partly a direct effect of hunger.Strong social hierarchies developed, larger fish nipping smaller ones more than the reverse. The correlation between size and hierarchical status was usually sufficient to account for the strength of hierarchy observed.Upon deprivation of food the dominant of any pair of socially unequal fish on the average increased its nipping of the subordinate. The nipping rate of dominants by subordinates did not change consistently; many low ranking fish decreased their nipping rate upon deprivation. These results would strengthen hierarchies during deprivation. Initiation of attacks by small fish, as opposed to nipping, increased consistently during deprivation.Nipping was more frequent between fish of equal status and size than between fish of unequal status or size. This could have accounted for the strength of hierarchies in groups in which the correlation between size and position was insufficient to do so.The increase in aggression upon food deprivation could function to increase the size of feeding territories when food is scarce. This and the strengthening of hierarchies would cause emigration of some fish from the area. Concentration of aggression between fish of equal size and status could permit parr of different ages to coexist.