Hidden in the ocean: The importance of detecting hybridisation in pelagic and deep-water fishes

The widespread occurrence of hybridisation in fishes suggests the need to revisit its importance for both a basic understanding of biological principles and practical applications for management and conservation. Despite evidence of its pervasiveness, the phenomenon of hybridisation in fish is not uniformly studied across species and environments. We note how natural hybridisation in pelagic and deep-sea fish has been rarely reported. For this reason, we carry out an analysis using both standard and phylogenetic comparative methods. Our results suggest a lack of evidence for the idea that pelagic and deep-sea fish are inherently less prone to hybridise. Likely, hybridisation and introgression are systematically underestimated in these groups. In light of this, we discuss why underestimation of hybridisation is problematic, and what may be done to ameliorate the situation. We propose scalable and cost-effective prioritisation, sampling and analysis strategies, to ease existing biases in assessing the impact of hybridisation among pelagic and deep-sea species and to ultimately improve the management and conservation – as well as basic biological knowledge – of these important species.