The effect of social interactions on circadian self-feeding rhythms in rainbow trout Oncorhynchus mykiss Walbaum.

Circadian feeding rhythms have been revealed in several fish species, but whether or not social interactions influence the expression of the rhythms remains largely unexplored. This paper reported such an exploration in rainbow trout. The experiment was conducted in two consecutive stages in two adjacent insulated rooms. In Stage 1, 40 fish (146.0+/-21.7 g, mean+/-S.D.) were held individually in Room 1. In Stage 2, those 40 fish from Room 1 were distributed into eight groups of five fish according to their previous circadian properties and placed in Room 2. Isolated trout were generally diurnal feeders, but variability among the individuals was evident, with five types of diurnal self-feeding pattern being detected. The influence of social interactions on diel self-feeding pattern in a group was found to be temporary and reversible. The grouping process did not necessarily enhance the expression of circadian self-feeding rhythms, and the dominant individual(s) did not determine the properties of circadian self-feeding rhythms in the group.