Elevated CO2 does not alter behavioural lateralization in free‐swimming juvenile European sea bass ( Dicentrarchus labrax) tested in groups

Rising concentrations of atmospheric carbon dioxide (CO2) equilibrate with oceanic CO2, contributing to ocean acidification (OA). OA can induce changes in fish behavioural lateralization (an expression of brain functional asymmetries) manifested in a left or right turning preference in detour tests. However, recent works find no such effects, and other work demonstrates assessment of turning preferences by detour tests to be a flawed methodology. Behavioural lateralization and OA effects on lateralization therefore need to be assessed with alternative paradigms. Here, we investigate left-right turning preferences of N=260 free-swimming juvenile European sea bass (Dicentrarchus labrax) reared in either: ambient conditions; OA conditions; or reared in ambient conditions but tested in OA water. Fish were observed free-swimming in groups of 10 individuals in a circular tank, and individuals’ turning preferences were quantified using trajectory data from video. In contrast to early studies, and in support of recent comprehensive work on coral reef fishes, we show that near future OA levels have no effect on behavioural lateralization (left–right turning preference) in juvenile European sea bass.

Methods
This data was collected by observing N=260 free-swimming juvenile European sea bass (Dicentrarchus labrax) (reared in either: ambient conditions; OA conditions; or reared in ambient conditions but tested in OA water) in groups of 10 individuals in a circular tank. Fish positions were recorded over a 1 hour period via an overhead Panasonic HDC-SD60 HD camera, with fish positions then quantified using idTracker and processed in Matlab as x-y cartesian co-ordinates relative to the circular tank (Collected by M Duteil in a previous experiment https://doi.org/10.5061/dryad.2dc8k)

Such coordinates were then converted into angles to reflect turning preference (Sea_Bass_ALL_Angles - paper). This was accomplished by taking a mean standard deviation in turn angle (76°) for all fish in all experiments when moving at speeds greater than 0.7 cm/s.