How Domestication Lowers Stress In Tamed Versus Wild Fish

Greg Howard
26th June, 2025

How Domestication Lowers Stress In Tamed Versus Wild Fish

Analysis of scale cortisol biomarkers reveals that domesticated strains of Common carp (Cyprinus carpio, left) and Atlantic salmon (Salmo salar, right) maintain significantly lower chronic stress levels than wild populations, supporting the hypothesis that domestication drives stress resilience.

Composite: Natural Science News / CC BY. [Sources]
Adapted from photos by:

Key Findings

  • A study by Bournemouth University and collaborators found domesticated common carp and Atlantic salmon show significantly lower and less varied chronic stress levels than their wild counterparts
  • Wild fish, however, display a much broader range of stress responses, including some individuals with very high stress, which may also be an adaptation to their unpredictable natural environments
  • This reduced stress variability in domesticated fish likely stems from selective breeding for traits beneficial in controlled settings, potentially making them less resilient to wild conditions
The domestication of animals, a process spanning centuries for many species, involves selective breeding to enhance traits desirable to humans. While often focused on characteristics like rapid growth or docility, this process can inadvertently alter fundamental biological responses, such as an animal's ability to cope with stress. This has significant implications, particularly for fish species like Atlantic salmon and common carp, which are widely farmed or used in recreational fisheries. When domesticated fish escape or are intentionally released into natural environments, their altered traits can impact wild populations, potentially introducing maladaptive characteristics. Recent research conducted by a collaborative team from Bournemouth University, University of Lodz, Muğla Sıtkı Koçman University, Ege University, South African Institute for Aquatic Biodiversity, Rhodes University, and Central Inland Fisheries Research Institute investigated these changes by comparing chronic stress levels in domesticated and wild populations of both common carp and Atlantic salmon[1]. The study focused on scale cortisol concentrations, which serve as a reliable biomarker for long-term physiological stress in fish. Cortisol is a hormone released in response to stress, and its levels in scales reflect an animal's chronic stress exposure over time. The findings revealed a distinct pattern. In both carp and salmon, individuals with low scale cortisol concentrations, indicating low stress sensitivity, were present across all sampled populations, whether wild or domesticated, and in natural or captive environments. However, fish exhibiting relatively high levels of scale cortisol were exclusively found among wild carp and wild salmon. This suggests that while domesticated fish are exposed to potentially stressful conditions in farms or angling ponds, they appear to possess a greater resilience against the adverse effects of chronic stress. In contrast, wild fish display a much broader range of stress responses, including some individuals that are highly sensitive to stress. The researchers also noted that these elevated cortisol levels in some wild fish might not solely indicate stress, but could also represent adaptive responses to the diverse and unpredictable challenges of their natural environments. This observed difference in stress response likely stems from the process of domestication itself. Selective breeding, a form of artificial selection, inadvertently favors traits that promote survival and productivity in controlled environments. For instance, in aquaculture, salmon are bred for rapid growth and efficiency in crowded tanks. Such breeding practices act as selective agents[2], where the environmental factors of farming (e.g., high density, handling, consistent food availability) lead to differential survival and reproduction. Individuals that are less stressed by these conditions, or perhaps inherently less sensitive to stressors, are more likely to thrive and pass on their genes. This can lead to a population with a reduced or altered stress response compared to their wild counterparts, who face a different array of selective pressures. The implications of these findings are significant, especially when considering the interaction between domesticated and wild populations. Previous studies on Atlantic salmon have shown that domesticated salmon grow much faster than wild salmon when reared together in fish tanks, but this growth advantage is largely diminished in rivers[3]. This earlier work demonstrated that underlying genetic differences in growth potential exist, but their phenotypic expression (how they look or behave) depends on the environment. Similarly, the stress resilience observed in the new study could be another genetically influenced trait that manifests differently across environments. A reduced stress response, while beneficial in a predictable farm setting, might be maladaptive in the complex and often harsh wild environment, where a robust stress response is crucial for navigating threats and resource fluctuations. The release of domesticated fish into natural environments, whether accidental escapes from farms or intentional stocking for recreational fishing, poses a well-documented challenge to the genetic integrity of wild populations[4]. Studies on Atlantic salmon have shown that even after several generations, genetic admixture from domesticated fish can lead to changes in life history traits, such as increased size and earlier maturation, which are often considered maladaptive in the wild[4]. The reduced stress variability found in domesticated fish in the current study could be another such maladaptive trait if it compromises their ability to cope with the diverse stressors of a natural ecosystem. However, the situation is complex. For common carp, research has shown that feral strains, even those recently derived from domesticated stocks, can rapidly re-adapt to wild environments, developing traits like more streamlined bodies, improved feeding skills, and greater caution towards predators[5]. This suggests that while domestication alters traits, there is a capacity for re-adaptation when fish return to the wild. The fact that wild carp in the new study exhibit high stress variability, including individuals with high stress sensitivity, aligns with the idea that they are adapted to a more heterogeneous and demanding environment. If domesticated carp with their lower stress responses were to become feral, it's possible that selection pressures in the wild would favor individuals with a more variable, or even higher, stress response, leading to a re-adaptation similar to other traits observed in feral carp[5]. Ultimately, this research highlights another critical way in which domestication alters fundamental biological attributes in fish. It underscores the potential for these changes, particularly in stress resilience, to have far-reaching consequences for the survival and evolutionary trajectory of wild populations when gene flow occurs. The findings reinforce the understanding that traits beneficial in a controlled, human-managed environment may not be advantageous, and could even be detrimental, in the dynamic and unpredictable conditions of the wild.

AgricultureHealthAnimal Science

References

Main Study

1) Domestication as the driver of lower chronic stress levels in fish in catch-and-release recreational fisheries and aquaculture versus wild conspecifics

Published 25th June, 2025

https://doi.org/10.1371/journal.pone.0326497

Related Studies

2) The ecological causes of evolution.

https://doi.org/10.1016/j.tree.2011.06.009

3) Cryptic introgression: evidence that selection and plasticity mask the full phenotypic potential of domesticated Atlantic salmon in the wild.

https://doi.org/10.1038/s41598-018-32467-2

4) Introgression of domesticated salmon changes life history and phenology of a wild salmon population.

https://doi.org/10.1111/eva.13375

5) Behavioural and morphological differences between feral and domesticated strains of common carp Cyprinus carpio.

https://doi.org/10.1111/j.1095-8649.2009.02345.x


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