Substrate-treated water: a method to enhance fish activity in laboratory experiments

Fast acclimatisation of experimental animals to laboratory test conditions is crucial for effective research. During highly standardized experiments, confounding parameters must be minimized, which might lead to animals behaving unnaturally. The objective of the present study was to develop a simple method to enhance activity of fishes under laboratory test conditions. Many fishes intensively interact with substrate in their natural environment; however, providing substrate during experiments might impair observation or may otherwise confound the results. Therefore, the behaviour of the cichlid Pelvicachromis taeniatus was examined in water that was exposed to substrate only prior to the experiment. As a control, fish behaviour in tap water was investigated. Fish activity (i.e. covered distance) was evaluated during a period of 2 h. In substrate-treated water fish were significantly more active than in tap water. Furthermore, males in the substrate-treated water increased their activity over time, whereas males in tap water did not. In contrast, activity of females did not change significantly over time. No significant relationship between fish activity and body size or condition was found. Furthermore, standard chemical water parameters were not altered by the substrate treatment. Thus, substrate is suggested as a means to improve the olfactory environment, promoting fish welfare and activity. In conclusion, this method is suggested as a standard with wide applicability across benthic fish species to improve acclimatisation of fishes to experimental conditions in the laboratory.