In a groundbreaking study that challenges long-held assumptions about fish welfare in recreational angling, researchers have found that domesticated common carp reared in aquaculture settings and used in catch-and-release fisheries exhibit significantly lower chronic stress levels than their wild counterparts. This paradigm-shifting research, published in PLOS One, underscores the complex physiological adaptations that emerge through domestication and raises important implications for fisheries management and animal welfare policies worldwide.
The investigation focused on measuring chronic stress by analyzing cortisol concentrations embedded within the scales of common carp (Cyprinus carpio). Cortisol, often referred to as the “stress hormone,” is a well-established biomarker reflecting the physiological stress response in vertebrates. Unlike acute stress, which manifests over minutes or hours, chronic stress develops over extended periods and can profoundly affect an organism’s health, behavior, and survival. The innovative method used in this study leverages the deposition of cortisol residues in fish scales over weeks to months, providing a retrospective and integrated marker of the fish’s stress experience.
Led by Professor Robert Britton at Bournemouth University, the research team meticulously compared cortisol levels in scales sampled from two cohorts: hatchery-reared carp regularly exposed to angling capture in managed recreational fisheries, and wild carp living free in their natural habitats with no exposure to capture by anglers. The study encompassed five recreational fisheries with domesticated populations and five ecologically comparable wild populations, allowing for robust cross-comparison. Intriguingly, despite the apparent stress of being caught repeatedly by anglers, the domesticated fish consistently demonstrated markedly lower chronic cortisol concentrations.
The disparity observed between the two groups was striking. While some wild carp exhibited scale cortisol levels overlapping with those of farmed fish, many wild individuals displayed cortisol concentrations that were upwards of tenfold higher. This finding suggests that the domesticated carp not only tolerate the episodic stress of capture-and-release but also maintain a physiological state indicative of reduced long-term strain. Such resilience is likely attributable to multiple factors inherent in domestication and controlled environments.
Domestication of common carp has long involved selective breeding wherein traits such as growth rate, disease resistance, and behavior have been optimized for aquaculture success. This study provides compelling evidence that chronic stress resilience has also emerged as a correlated response to domestication. Domesticated carp strains might possess altered hypothalamic-pituitary-interrenal (HPI) axis regulation, resulting in dampened cortisol synthesis or enhanced cortisol clearance. These endocrine modifications may confer adaptive advantages in heavily managed fisheries where frequent human interaction occurs.
Moreover, the environmental context in which domesticated carp exist differs substantially from that of wild populations. Recreational fisheries typically provide abundant food through angler baits and controlled conditions, relieving pressures related to food acquisition and predation risk. Wild carp, by contrast, must invest considerable energy in foraging across heterogeneous and sometimes resource-poor habitats. This increased activity and environmental unpredictability may chronically elevate cortisol production as part of their generalized stress response.
The research team also warned against overgeneralization. While hatchery-reared carp show encouraging signs of stress tolerance, fish welfare in recreational fisheries is multifaceted and requires continued vigilance. Chronic stress is but one axis of health assessment; disease prevalence, water quality, temperature fluctuations, and injury rates remain critical parameters to monitor. This is especially urgent under current global climate change scenarios where rising temperatures can exacerbate physiological stress and pathogen susceptibility.
Co-author Dr. Josephine Pegg of the South African Institute for Aquatic Biodiversity emphasized the wider significance of the findings within the global socio-economic landscape of recreational fisheries. Such fisheries generate billions of dollars annually and support livelihoods across continents. Balancing economic benefits with ethical stewardship of fish welfare mandates rigorous scientific inquiry, and this study exemplifies that imperative. It also calls for integration of physiological measures like scale cortisol analysis into routine fishery management protocols.
This research further contributes to a nuanced understanding of stress biology in teleost fish, emphasizing the need to distinguish between acute and chronic stress impacts. Capture-induced acute stress responses, often marked by transient spikes in plasma cortisol, are well documented and have spurred improvements in catch-and-release methodologies to minimize mortality. However, the chronic dimension — capturing the cumulative energetic and immunological toll of repeated stress exposure — has been comparatively understudied, until now.
Importantly, the scale cortisol approach presents a non-lethal, minimally invasive technique enabling longitudinal monitoring of individual fish stress states. This methodological advance opens new avenues for ecological and physiological studies that can inform selective breeding programs, conservation strategies, and welfare assessments. Its application can extend to diverse species subjected to both anthropogenic and environmental stressors.
In synthesizing these findings, one must recognize the evolutionary and ecological consequences of human-mediated selection pressures. Domesticated carp exhibiting reduced chronic stress may outperform wild conspecifics under artificial conditions but could face fitness disadvantages should they escape into natural ecosystems. Understanding these trade-offs constitutes a critical frontier for fisheries science and conservation biology.
In conclusion, this landmark study offers rigorous evidence that domestication drives lowered chronic stress levels in common carp within catch-and-release recreational fisheries and aquaculture, setting the stage for improved welfare practices and sustainable management. By illuminating intrinsic physiological differences between farmed and wild fish, it dispels misconceptions about the detrimental impacts of angling capture in controlled contexts and directs attention to broader welfare considerations. As global fisheries continue to evolve, integrating such scientific insights will be pivotal in harmonizing human use with ecological stewardship.
Subject of Research: Animal tissue samples
Article Title: Domestication as the driver of lower chronic stress levels in fish in catch-and-release recreational fisheries and aquaculture versus wild conspecifics
News Publication Date: 25-Jun-2025
Web References:
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0326497
http://dx.doi.org/10.1371/journal.pone.0326497
Image Credits: Bournemouth University
Keywords: Fish, Organismal biology, Wildlife, Marine biology, Ecology, Freshwater biology, Earth sciences, Conservation ecology, Natural resources management, Wildlife management, Biodiversity conservation, Aquaculture, Fisheries management
