Applied Animal Behaviour Science 163 (2015) 188–193 Contents lists available at ScienceDirect Applied Animal Behaviour Science journa l h om epa ge: ww w.elsevier.com/locate/applanim A conditioned response overrides social attraction in common carp: A possibility for low stress sorting strongly schooling fish? Flavia Oliveira Mesquita, Fabio Luiz Borcato, Felicity Ann Huntingford ∗ Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK a r t i c l e i n f o Article history: Accepted 23 November 2014 Available online 3 December 2014 Keywords: Common carp Conditioning Self-feeding Low stress Movement control a b s t r a c t In this study we investigated whether a conditioned response to a light cue can override the strong schooling tendency of common carp, with a view to identifying a possible system for low stress control of movement for captive fish. Carp were trained in groups of three to approach and bite a trigger to obtain food, the trigger being located next to a coloured light. In an initial pre-training period, fish were trained to approach and feed from a single trigger, identified by either a red, a green or a blue light; six groups were pre-trained with each colour. During 10 pre-training trials, 11 of the 18 groups learned to feed efficiently in this set up. These groups were then given further training with triggers at three potential feeding locations, again identified by red, green and blue lights, food being delivered from the trigger signalled by the colour on which the fish had been pre-trained. The position of the rewarded trigger was changed randomly between trials, which numbered 15 in all. All 11 groups learned to approach the rewarded trigger preferentially, though some sampling of unrewarded triggers continued. The learned response was strongest for fish trained to approach the red light. New groups were then constructed comprising one fish trained to each of the three colours. When released simultaneously in a position equidistant from a red, a green and a blue light, all unrewarded, the three fish swam independently towards the colour on which they had been trained. Besides confirming the ability of common carp to use a demand-feeding system and to associate a coloured light with the presence of food, these results show that individual fish can be induced to move away from a small group towards a coloured light as a result of differential training. The potential for using this capacity to control movement of common carp held in captivity, for whatever reason, is discussed. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Given the adverse effects of stress on growth, health and welfare in captive fish (Huntingford et al., 2012), it is ∗ Corresponding author at: College of Medical, Veterinary and Life Sci- ences, University of Glasgow, Glasgow G12 8QQ, UK. Tel.: +44 141 945 0404. E-mail address: Felicity.Huntingford@glasgow.ac.uk (F.A. Huntingford). important to minimise stress in fish-husbandry systems. Rearing fish in captivity for whatever purpose often involves periodic sorting into categories, for example, on the basis of size, gender or reproductive condition. It is also sometimes necessary to separate specific individuals from within a group. A number of techniques have been proposed for reducing handling stress during such pro- cesses (Lines and Frost, 1999; Zion, 2012), some based on innate responses to directional cues. For example, innate positive phototactic and rheotactic responses of guppies http://dx.doi.org/10.1016/j.applanim.2014.11.014 0168-1591/© 2014 Elsevier B.V. All rights reserved.