Studies in Mass Physiology: The Effect of Numbers upon the Oxygen Consumption of Fishes

Abstract

The study of animal aggregations during the past few years in this and other laboratories has uncovered a large of interesting and valuable facts concerning the reactions and relations of animals when placed with others of their kind. This body of data has recently been reviewed by Allee ('31). Evidences of a group have been based upon such things as growth, reproductive rates, survival under toxic conditions, and other similar indices. In the fishes there has been some work on the effects and causes of aggregations. Church* ('27) has shown that the growth of certain tropical fishes is conditioned to a considerable extent by the number of individuals present in the aquaria. The retardation of growth when larger numbers were present was ascribed to the presence of accumulated excretory products. Other workers have come to the same conclusions concerning the effects on growth produced by crowding of fishes (Willer and Schnigenberg, '27; Kawajiri, '28). Much of the work on fish aggregations has dealt with species which ordinarily form schools in nature. Such aggregations seem distinctly different from the vast majority of fishes which do not appear to have the schooling instinct. An interesting problem presents itself in bridging the gap between the solitary forms and those which exhibit highly integrated mechanisms of aggregation. It was thought probable that even in fishes which show no schooling reactions but which tolerate the nearby presence of other fishes there may be some measurable physiological effect of grouping or crowding other than the effects of growth, knowledge of which would open the way to further investigations upon the general problem of aggregations. Such effects have already been reported. Welty ('30) has shown that in goldfishes, which have not been considered as social, there are differences in learning behavior according to whether the fishes are single or in groups. Thus, it may be that even in animals which have hitherto been thought of as non-schooling, or non-social, there are influences producing effects which have so far been either overlooked or neglected.