Fish farming techniques are designed to enable animals to fulfill their maximum growth and development potential. To this end, it is necessary to provide them with optimal living conditions. Because it can strongly impair fish performance, stress is a major risk to consider in aquaculture. It is important to measure the stress impact in order to better anticipate its consequences. What is the impact of stress on fish? How can the resulting risks be controlled at the farm level?
A stressed animal is more vulnerable to pathogens
Stress is a normal reaction of the organism to a perceived or potential danger, in which the bodily processes prepare for “fight or flight”. Throughout their lives, farmed fish usually undergo various stressful episodes.
These episodes may be of two types:
- Acute: the most common sporadic factors of stress in aquaculture are transport, manipulation (sorting, vaccinations, partial fishing ...), and sudden changes in water quality (water safety, oxygenation, composition);
- Chronic: these can be triggered by the continuing presence of a xenobiotic in water, overcrowded ponds, a non-homogeneous population, uneven feed distribution, inadequate oxygenation, or the presence of predatory birds perched on cages or on the shores of farming units.
Stress is likely to disrupt the delicate balance between the animal’s defense abilities, the quality of farming conditions, and the pressure exerted by potential pathogens on the environment. The disturbance of this precarious order favors the irruption of diseases and dysfunctions.
Animal’s tolerance of stress depends on the nature and intensity of the reaction aroused. This impact varies depending on the nature of the stress, the animal’s species and strain as well as its experiences and health condition.
It has been proven that a healthy animal will more efficiently face a stressful event (see diagram) than a weak animal. Several experiments have also highlighted the negative effects of stress on an animal's ability to fight against pathogens in its environment.
What are the stress parameters in fish farming?
In order to become a tool, stress should be measurable. It is necessary to measure the stress response in order to anticipate its consequences. The occurrence of stress will cause various types of responses:
- Hormonal: cortisol, catecholamines...;
- Metabolic: increase in oxygen consumption, changes in the blood’s salt concentration;
- Behavioural: grouping of fish, increased swimming speed.
It is more or less easy to quantify these indicators. Once the extent of stress is assessed, its effects can be categorized by analyzing the level of the response triggered:
- A first level of response relates to a light and short-term stress. These episodes of stress can trigger the release of hormones that put the body in a state of high alert. If they don’t recur too often, their impact on rearing performance is moderate to non-existent.
- A second level, resulting from a longer exposure to a more intense form of stress, will compel the animal to mobilize its resources in order to cope with the ensuing metabolic demand. At this level of exposure, stress has a definite impact on the productivity of the population in question.
- The third level marks a prolonged exposure to a very high level of stress. This level corresponds to the point beyond which the fish’s resources are no longer sufficient to efficiently fight against the perturbation endured.
The Techna Group experts can assist fish farmers in their continuous improvement of fish comfort, performance, and fish ability to cope with stress. For more information, please contact our experts!
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