
A pioneering study has shown that understanding circadian rhythms and age-related differences in stress responses has the potential to change the perception of fish welfare practices in aquaculture and laboratory settings.
Published in the Journal of Experimental Zoology Part A by an international team of researchers, the study investigated how stress responses in zebrafish (Danio rerio) vary with age and time of day. Using two standard behavioural tests—the open-field test and the diving test—the researchers uncovered significant differences in how juvenile and adult zebrafish respond to stress over a 24-hour period.
The results revealed that juvenile zebrafish experience heightened stress responses during the night, whereas adults are more stressed during the daytime. While these findings align with natural circadian rhythms, they highlight an area that has been largely overlooked in non-mammalian species until now.
Juveniles consistently exhibited greater sensitivity to stress than adults in most behavioural tests, emphasising the critical role of developmental stages in determining how fish respond to environmental challenges.
Key behavioural indicators, including freezing, erratic swimming, and thigmotaxis (staying near the edges of a space), varied not only with circadian timing but also with age, offering valuable insights for improving fish welfare.
The study underscores the importance of tailoring aquaculture practices to align with circadian and developmental patterns. For example, synchronising stressful procedures such as transport, feeding, and handling with periods of lower stress susceptibility could significantly reduce physiological strain on fish, thereby promoting their health and growth. Similarly, laboratory experiments would benefit from being conducted at times when stress responses are naturally subdued, ensuring more reliable and consistent results.
These findings could inform age- and time-specific welfare protocols across various species. For instance, juveniles, which are more stress-sensitive at night, may require enhanced care during nocturnal hours. Conversely, adults, who experience greater stress during daylight hours, could benefit from handling and feeding schedules designed to minimise disturbances during this period.
The researchers also call for further investigation into the physiological mechanisms underlying these patterns, particularly the roles of stress hormones and the circadian clock.
With aquaculture expanding as a sustainable food source, understanding fish biological rhythms could lead to both ethical and efficient practices. Furthermore, zebrafish, a widely used model organism, can provide a foundation for applying these insights to other species.
As the aquaculture industry seeks to balance productivity with ethical responsibility, studies like this provide a roadmap for incorporating biological insights into routine practices. This approach not only ensures healthier and less stressed fish but also contributes to a more sustainable and humane industry.