(a) The default arena design consists of two CNS-milled plastic (or metal) parts, holding between them a glass coverslip of 9 mm in diameter (1 mm height) that can be easily exchanged between experiments. Shown here is a version used in the experiments of Figures 1-3 that has a central divider separating the arena in two compartments into which compounds can be delivered via diffusion from two quadratic reservoirs (b) The picture shows the illuminated arena. (c-e) The system allows for long-term recording over several hours in which case the water level (75-100 μL) can be kept constant by compensating for evaporation. This can be easily achieved via a syringe pump (green) as shown in the photograph. (f) A 150 mm travel path x-stage is incorporated into the system to move a (g) commercial multiwell-slides with 18 holes (5 mm diameter each) positioned by a custom-made 3D printed holder. We showcase the use of this configuration for sorting zebrafish based on their expression level of GCaMP5g (+ and – in the upper fluorescent image).