Human infants and non-human animals can discriminate the larger of two sets of discrete items. This quantity discrimination may be based upon the number of items, or upon non-numerical variables of the sets that co-vary with number. We have demonstrated that angelfish select the larger of two shoals of conspecifics without using inter-fish distance or space occupied by the stimuli as cues. However, density appeared to influence the choice between large shoals. Here, we examine the role of another non-numerical cue, swimming activity of the stimulus fish, in quantity discrimination by angelfish. To control this variable, we varied the water temperature of the stimulus aquaria or restricted the space occupied by each fish in the stimulus shoals. We used the previously successfully discriminated contrasts consisting of large (10 vs. 5) and small (3 vs. 2) shoals. We also studied whether more active or less active shoals are preferred in case of equally sized shoals (10 vs. 10, 5 vs. 5, and 3 vs. 3). When differences in stimulus fish activity were minimized by temperature manipulation we found angelfish to prefer the larger shoal in the 3 vs. 2 comparison, but not in the 10 vs. 5 comparison. When activity was controlled by space restriction, angelfish preferred the larger shoal in both numerical contrasts. These results imply that the overall activity level of the contrasted shoals is not a necessary condition for small shoals discrimination in angelfish. On the other hand, the results obtained for the large shoals, together with results obtained in the control treatments (equal numerical contrasts and differing activity levels), suggest that activity is a sufficient condition for discrimination when large shoals are involved. Further experiments are needed to evaluate the influence of other continuous variables, and to assess whether the mechanisms underlying performance are comparable to those suggested for other animals.
Keywords: quantity discrimination, continuous variables, swimming activity, angelfish, shoal choice, numerical cognition
Citation: Gómez-Laplaza LM and Gerlai R (2012) Activity counts: the effect of swimming activity on quantity discrimination in fish. Front. Psychology 3:484. doi: 10.3389/fpsyg.2012.00484
Received: 30 July 2012; Accepted: 20 October 2012;
Published online: 12 November 2012.
Edited by:Christian Agrillo, University of Padova, Italy
Reviewed by:Angelo Bisazza, University of Padova, Italy
Copyright: © 2012 Gómez-Laplaza and Gerlai. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
*Correspondence: Luis M. Gómez-Laplaza, Department of Psychology, University of Oviedo, Plaza de Feijoo s/n, 33003 Oviedo, Spain. e-mail: email@example.com; Robert Gerlai, Department of Psychology, University of Toronto Mississauga, 3359 Mississauga Road North, Room 3035, Mississauga, ON L5L 1C6, Canada. e-mail: firstname.lastname@example.org