Zebrafish (Danio rerio) are widely used in laboratories around the world. Despite this, their welfare in laboratory conditions has not been widely studied. Net-handling of zebrafish has been found to cause physiological stress and anxiety-like behaviour, yet there are limited studies exploring other handling methods. The aim of this project was to compare anxiety-like responses in zebrafish handled by net versus scoop, where fish are not exposed to air. Anxiety was measured through preferences to black versus white sides of a tank as well as preferences to the lower versus upper half of the tank. These are established measures used in pharmacological research. Anxious zebrafish tend to prefer the bottom and the dark side of the tank. Additionally, measures of velocity (movement in centimetres per second) were included as high velocity has been found to indicate anxiety.

Net-handled zebrafish visited the two bottom compartments at a higher frequency than scoop-handled fish during most of the observation (between 5-20 minutes). Additionally, net-handled zebrafish had higher velocity between 10-15 minutes. Scoop-handled zebrafish spent more time during each visit to the upper black side of the tank in the beginning and middle of the observation compared to net-handled zebrafish. These results suggest that net-handling causes more anxiety to zebrafish than scoop-handling, though further research is needed. Less anxiety caused by external factors is particularly important when using zebrafish in research related to anxiety or anxiolytic/anxiogenic medication, where anxiety responses could affect data quality. Therefore, a less anxiety-inducing handling method can not only improve the welfare of the millions of laboratory zebrafish around the world, but also improve the quality of research conducted on zebrafish. Because scoop-handling zebrafish caused less anxiety-like behaviour, this method should be considered in laboratories.