Differing selective effects on body size, swimming performance, and behaviour by passive and active fishing gears in an artisanal fishery
Description
Harvesting can selectively remove individuals with certain traits, driving phenotypic changes in wild populations. Fishing gear type can also influence which traits are targeted, shaping selection direction. While trait-based selection has been studied in commercial and recreational fisheries, its role in small-scale artisanal fisheries, such as the ornamental trade, is virtually unknown. We reveal how different artisanal gears target behavioural and physiological traits in wild cardinal tetra (Paracheirodon axelrodi), a species central to this trade. Fish were collected in the Amazon Basin using passive (traps) or active (nets) gears and tested under controlled laboratory conditions. Swimming performance was quantified via a constant acceleration test, and behavioural phenotypes (risk-taking, exploration, activity, and social cohesion) were assessed using open field, novel object, and maze assays. Trap-caught fish were larger and exhibited lower relative maximum swimming speeds than net-caught fish. Behavioural differences emerged but were assay-specific: trap-caught individuals showed greater risk-taking in the maze test, whereas net-caught fish were faster and more cohesive. Ambient temperature strongly influenced behaviour, increasing activity and exploration while reducing cohesion, underscoring sensitivity to climate change. These findings are among the first to provide evidence that artisanal gears can impose selective pressures across multiple phenotypic traits, with potential consequences for evolution and conservation. These findings also highlight the importance of considering assay design and environmental conditions when measuring behaviour.