What effect does stress have on Koi?

Fish kept under controlled conditions, such as seen in aquaculture, in the ornamental fish breeding sector, in zoo’s and at home, are subjected to a variety of conditions that are not present in their natural environment. In aquaculture production, fish have to deal with a wide range of management practices that potentially cause (chronic) stress including but not limited to stocking density, water quality, system design, feed quality and handling processes such as grading, sampling and transportation.

It is well recognised that stress, in particular chronic stress, affects the overall performance and health status of fish. Chronic stress leads to immune suppression, decreased chances reproduction and increased mortality. In this framework, fish welfare has also gained interest of consumers during the last decade.

It will also be the case in sport fishing {well-being} of fish.

A similar situation exists for ornamental fish reared in specialized farms (e.g. koi), kept in zoo’s and at home. Also here the public concern and debate on welfare of ornamental fish and even in sport fishing is increasing rapidly. However, compared to aquaculture species, relatively little scientific research has been conducted on how chronic stress influences fish health and welfare in these sectors.

The effect of chronic stress on pigmentation and overall health

For a successful, more sustainable and fish welfare-minded management in production, zoo’s and home aquaria, disease prevention is one of the most critical elements. Hereby, recognizing that the actual development and the risk of a disease outbreak is the result of a complex interaction between the host, its environment and the pathogens is of utmost importance (Fig1). In addition, it has been demonstrated that stress influences pigmentation, though, the cellular mechanisms underlying the relationship between stress and colour expression remain largely unknown. Quantification of stress, in particular of chronic stress (Aerts et al. 2015), in ornamental fish is subsequently of utmost importance.


The interaction between the host, (potential) pathogens and the environment (adjusted from Snieszko, 1974) shows that stress induced higher glucocorticoid levels increase the risk of diseases, hereby affecting various actors represented by the area of the overlapping circles. Some major factors relevant in (chronic) stress reduction are listed for each of these areas.

A variety of potential stressful stimuli will always be present.

A variety of potential stressful stimuli will always be present. However, preventing chronic stress and optimizing the stress response to commonly encountered practices and as such by optimizing the stress resilience of the fish to these practices are of utmost importance in a more sustainable and profitable sector for ornamental fish. Furthermore, fish kept in a ‘chronic stress free’ environment ‘score high’ for fish welfare in certification standards.

beautiful koi, traditional ornamental fish in pounds


Aerts J, Metz JR, Ampe B, Decostere A, Flik G, De Saeger S (2015) Scales Tell a Story on the Stress History of Fish. PLoS ONE 10(4): e0123411.

For more information

Stress Physiology Research Group (StressChron)

Ghent University and Flanders Research Institute for Agriculture, Fisheries and Food

Wetenschapspark 1, 8400 Ostend, Belgium

Email: info@stresschron.eu

Website: www.stresschron.eu

About Editors

The Editorial Board is the melting pot of writers and authors within Team KoiQuestion. It places approved reporting from a general perspective or from an external source. Questions or tips for the editors? email to redactie@koiquestion.com

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