UBC Theses and Dissertations
Colour matters : coho salmon (Oncorhynchus kisutch) prefer and are less aggressive in darker coloured tanks Gaffney, Leigh Phillippa
Fish are capable of colour vision and certain colours have been shown to affect growth and survival, skin colour, stress response, and reproduction. Beyond these physiological consequences, colour has also been shown to affect aggression levels, which is a widespread problem in aquaculture. The compatibility of fish with tank colour has been largely neglected within the aquaculture industry. Common practice is to use light blue tanks but there is no scientific basis for this choice. Closed containment aquaculture systems provide a good model to investigate the effects of tank colour on fish. Though closed containment aquaculture systems provide the opportunity for full control of environmental conditions, little research to date has investigated which parameters within these systems promote fish welfare. The aim of this study was to assess preferences of coho salmon for tank colour and determine the effects of colour on aggression. Coho salmon (n=100) were randomly assigned to 10 tanks, each bisected to allow fish to choose between two colours. Using a Latin-square design, each tank was tested with each of the following colour choices: blue vs. white, light grey, dark grey, and black, as well as black vs. white, light grey, dark grey, and a mixed dark grey/black pattern. Fish showed a strong preference for black over all other tank background options (p < 0.0001) with the exception of pattern, which was still significant but slightly less strong (p < 0.01). Moreover, darker colours in the environment resulted in lower rates of aggressive behaviours compared to lighter colours (p < 0.0001). These results present the first evidence that darker tanks are preferred by and decrease overall tank aggression levels in salmonids.
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