Heart trouble and personality in stressed fish

Janne Karin Brodin

Stress can cause damage to important biological systems in the body, and so lead to illness. How great the stress-induced damage becomes depends on individual ability to cope with stress, and the body’s reaction to stress.

Ida Beitnes Johansen Photo: Janne Brodin

Biological systems such as the central nervous system and the cardio-vascular system (heart and blood vessels) may be negatively affected by stress. In her thesis, which she defended on March 18th 2011, PhD student Ida Beitnes Johansen shows that fish that produces high levels of the stress hormone cortisol have a more pronounced stress reaction that fish that produce lower levels of cortisol.

The cortisol hormone is produced in the adrenal glands during stress, and has been shown to be involved in most stress related illnesses in humans, fish and other animals. The capacity for producing the stress hormone is highly inheritable.

Fish with different stress hormone productions
A research programme has developed two strains of rainbow trout, where one of the strains reacts far more to stress than the other one. These fish strains produce different levels of cortisol when they are exposed to stress. Beitnes Johansen used these two strains to conduct a series of studies. She has studied behavioural, physiological-anatomical and molecular reactions to stress.

Differences in behaviour
The results show that fish that react little to stress are often socially dominant, have routine forming behaviours and depend on learned information, such as where they will find food. These fish also display a high expression for a type of cortisol receptors, or receptors in the brain, that are important for learning and remembering.

Fish that are sensitive to stress and produce more cortisol have more flexible behaviours, and adjust their behaviour to their situation. Varying degrees of neoformation of nerve cells in the brain is also shown to be important for this variation in learning, memory and routine formation.

Larger hearts
It was also shown that fish with an inherited high cortisol response had larger hearts. These finds are made in collaboration with a group of specialists on heart failure at Oslo University Hospital, Ullevål. The results are very similar to what is seen in humans with cardio-vascular problems.

The results show that there is a pronounced link between variations in behaviour, stress response and organ function in stressful situations.

Updated: 13.04.11
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