In the fish lab at university individuals of various fish species are being kept. Flounders, eels up to mudskippers are in our scientific focus there. Besides behavioural experiments, in which we showed that fishes can be conditioned very well, the method Particle Image Velocimetry (PIV) is mainly used to examine e. g. the breathing current or escape responses of the fishes. PIV allows to measure and analyse small scale water movements.