Substrate colour guides turquoise killifish's (Nothobranchius furzeri) choice of preferred spawning habitat.

Turquoise killifish (Nothobranchius furzeri) is a promising new model species used in biomedical and ecological laboratory experiments, and should be kept under optimal conditions to ensure fish welfare and the quality of science. While the popularity of this model species is rapidly increasing, we need to improve our understanding of how the species interacts with its environment in order to optimise its husbandry. Specifically, turquoise killifish are substrate spawners that bury their eggs in the sediment which can be accommodated under captive conditions, but it is not yet known whether or not turquoise killifish have a preference for a specific sediment colour. Here, we performed a laboratory experiment in which fish could choose between white, orange, and black sand for spawning, colours of which are relevant in both laboratory and field conditions. We assessed their preference in the context of single breeding pairs, as well as in a social group setting. Additionally, we also assessed preference of individuals for a white vs. black background in a non-mating context. Single breeding pairs deposited over 3.5× more eggs in black compared to orange or white sand. Similarly, fish in social groups deposited over 3.5× more eggs in black compared to orange sand, which in turn was over 2× times higher than that in white sand. Fish showed a slight preference for the black compared to the white zone in a non-mating context but this did not correlate with substrate choice during the spawning tests. The results suggest that turquoise killifish select their preferred spawning location based on the colour of the substrate. These findings contribute to our understanding of the species' biology and can help to guide good welfare and scientific practice. This article is protected by copyright. All rights reserved.