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Manage Stress to Improve Welfare

Fish Welfare & Stress Reduction

Welfare is a complex and multifaceted subject involving scientific, ethical, economic and religious dimensions. Animal welfare is often defined by how an animal copes with the conditions it lives in. An animal is in a good state of welfare if it is healthy, comfortable, well nourished, and able to express innate behaviour whilst not suffering from unpleasant states such as pain, fear, or distress. In aquaculture, consideration of animal welfare is now fundamental when making decisions on daily husbandry practices, and when choosing production systems.

welfare block

There are a range of welfare indicators to consider when assessing welfare. These indicators should be species-specific, reliable, feasible and quantifiable. They should also provide information on the extent to which the animal’s welfare needs are being met. While there is no set framework for assessing welfare in fish, there are four distinct categories of welfare indicators which provide:

    1. Health status – Injury, disease status and immune response
    2. Physical status – Growth, respiratory rate
    3. Physiological status – Stress hormones
    4. Behavioural status – Food intake, swimming, aggression / hierarchy

Welfare Concerns in Aquaculture

Feeding:  Failure to provide an appropriate diet in an attractive form may result in growth issues. Failure to provide the right amount of food at the right time may result in population hierarchy and malnutrition.harvest

Health:  Fish are routinely treated and vaccinated to prevent and manage diseases within populations. Health treatments typically involve crowding, handling and other adverse conditions that will cause stress and damage to individuals. For some disease treatments, brain damage is known to occur.

Grading:  Fish are graded to produce like-sized groups for efficient husbandry and to prevent aggression/hierarchy. Grading involves crowding and handling that will cause stress and damage to individuals.

Transport:  Fish are routinely transported from tank to tank or from site to site. Transport involves crowding, handling, changing water quality and other adverse environmental conditions that will cause stress and damage to individuals.

Stocking density:  Stocking densities that are too high can have negative effects on welfare. High stocking density results in reduced growth, aggression, and an increase in fin erosion and external damage.

wildSlaughter:  Fish are slaughtered following the production cycle prior to human consumption. Slaughter practices involve handling, crowding, and in some cases, pain. Muscle quality is severely affected when the slaughter operation is poorly managed. For any stunning/killing method to be considered humane, it is critical to demonstrate that it actually kills the animal, or at least causes unconsciousness that lasts until death. If the method does not cause an immediate loss of consciousness, then it is also necessary to demonstrate that it does not cause pain or distress before the animal becomes unconscious.

The Link Between Stress and Welfare

It is widely accepted that fish experience stress. Stress is a regular and undesirable aspect of aquaculture production and has serious welfare implications. Common aquaculture stressors involve changes to the fish’s immediate environment. These fit into three main categories:

Chemical changes: Contaminants, low oxygen, acidification
Physical changes: Handling, capture, confinement, vaccination, transport
Perceived threats: Startling, predators

Stress is a non-specific physiological response composed of primary, secondary and tertiary responses. When fish perceive stress, they respond with the release of hormones into the blood. This is known as the primary response to stress. These hormones elicit a secondary response characterised by changes to the metabolic rate and immune system which ultimately impact on growth, resistance to disease, behaviour, and in some cases, survival (tertiary response). These tertiary responces are known welfare indicators.  Assessment of the stress response iself can be quantified and used as welfare indicators.

AQUI-S® Can Improve Welfare!

Managing stress is critical to maintaining good welfare. AQUI-S® can be used to reduce stress at all stages of aquaculture. AQUI-S® is a gentle-acting aquatic anaesthetic that works by inhibiting nerve axons and membrane potential actions. This results in a widespread depression of the central nervous system (CNS) which in turn inhibits or limits the release of the stress hormones, cortisol and the catecholamines (e.g. adrenaline), from the hypothalamic-pituitary-interrenal (HPI) axis. Inhibiting the release of these hormones means there are no secondary stress responses or whole-body tertiary responses. As such, physical injury is reduced, growth rates are sustained, and the immune system is maintained following the stress event. Depending on the application, survival is also improved when AQUI-S® is used.

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