Colour preferences of juvenile turbot (Scophthalmus maximus)

- A new method to study the self-referent colour preference of fish.
- First report on the background colour preference of juvenile turbot.
- Long-term adaptation did not alter colour preferences of turbot.
- Turbot displayed a preference for a white background and a dislike for black, red, or brown backgrounds.
- Self-referent colour preferences related to the optimal growth.

The background colour of aquaculture tanks is normally chosen based on practical experience and/or observations of fish behaviour and the growth rates achieved. However, some farmed species, including turbot, are sentient and can show a preference for a particular environment. In the current study, a self-referent colour preference device was developed and the self-referent colour preference of farmed fish investigated. In experiment 1, the background colour preference of juvenile turbot cultured under a grey background for > 3 months post-incubation was evaluated. Based on these results, in experiment 2, juvenile turbot were adapted to blue, pink, white, or black backgrounds for 50 days and their preferences established. Meanwhile, the growth rates, feed intake, and metabolic rates (including oxygen consumption rate, and ammonia excretion rate) of the turbot were evaluated. The results showed that turbot farmed under a grey background, or after long-term white, blue, pink and black colour adaptation, always displayed a preference for a white background and a dislike for black, red, or brown backgrounds, although their body colour was greyish. Long-term adaptation influenced the frequency of juveniles selecting white, black, pink or blue backgrounds. They showed the highest growth rate, feed intake, and metabolic rates under blue and white backgrounds, and the lowest under a black background in accordance with their preferences shown in experiment 1. Although it is unclear how turbot determine their self-referent colour preferences over such a short period of time, these results indicate that dark colours are unsuitable for the aquaculture of turbot culture in terms of the welfare of the fish.