Positioning behaviour in fish shoals: a cost–benefit analysis

Shoal position can have a strong influence on individual fitness. Individuals in front positions of shoals were observed to have higher feeding rates than individuals elsewhere. Manipulation of nutritional state showed that hungry individuals had a stronger preference for front positions and that the duration of food-deprivation was positively correlated with the degree of the position preference. On the other hand, front positions (like other peripheral positions) probably incur costs in terms of increased predation risks. Experiments with Schreckstoff showed that frightened individuals seek the central part of the shoal. This suggests that individuals rotate their shoal positions according to the tradeoff between energy intake and predation risk.