The presence of substrate as a means of environmental enrichment does not improve the welfare of the laboratory rare minnow (Gobiocypris rarus).

Increasing the complexity of physical structure is a common means of environmental enrichment, and it is possible to improve the welfare level of fish by improving their biological function. Although laboratory fish play an important role in the field of life sciences, their rearing environment usually does not have any enrichment measures. In this study, sand was added to the bottom of the rearing tank as the treatment group and its effect on the laboratory rare minnow (Gobiocypris rarus) was comprehensively assessed through growth, behaviour and physiological indexes. The results showed that there were no significant differences in growth, anxiety-like behaviour or dopamine, serotonin and their metabolites between the control group and the treatment group. In general, no obvious benefits were found from the presence of sand substrates, and it is not recommended as a measure to enrich the environment of the laboratory rare minnow.