Live fish are often transported both short and long distances, for example, as farmed fish from hatcheries to on-grow fish farms, as ornamental fish that are being collected in the wild, or when experimental fish species are shipped between laboratories. The zebrafish (Danio rerio) is a popular research animal used globally in the fields of life science, such as toxicology and neuroscience. Despite the fact that zebrafish are commonly transported both nationally and internationally, it is still not fully known how transporting zebrafish affects their welfare. To better understand the short- and long-term physiological and welfare effects of transporting zebrafish, we performed a series of experiments transporting adult zebrafish.
Fish transport experiments were repeated five times. Adult wildtype zebrafish were raised at a zebrafish core facility in Stockholm, Sweden and transported to our research facility in Gothenburg, Sweden, a journey that took around 6 hours by car. Animals were packed for the transport in plastic bags (20 fish per bag) according to commonly used standard operations procedures. Upon arrival, the transport water was collected for analysis of water quality and content of the stress hormone cortisol that was measured using a radioimmunoassay. After being acclimatized to the new facility the fish were transferred to tanks with fresh aquarium water, and kept up to nine days during which the water was collected for analysis.
Our experiments showed that all the fish survived the journeys and the acclimatization period. However, water cortisol levels in the transport bags after the transports were on average 0.1 ng/ml, which is higher than cortisol levels normally measured in their aquaria. One day after the transport, the cortisol levels showed large variations between the home tanks, but had dropped to about a tenth of the transport concentrations (Figure 1). After the transport experiment, the water cortisol levels remained elevated until five days, when they were significantly lowered. This indicates that packing and transporting of adult zebrafish induce an elevated secretion of cortisol in the water, which could be a sign of both acute and long-term stress.
More research is needed to better understand the welfare implications of the elevation of secreted cortisol, but we foresee that our findings could have implications for the aquaculture and transport of other fish species, for example, farmed or ornamental fish.