Salmon's body language tells all: Body language can be an indicator of stress or well-being in fish

Researchers at the Institute of Marine Research in Bergen and Nofima Marin in Tromsø have been collaborating on finding methods of measuring the stress levels and welfare of production fish.

"One aim of our project was to determine if fish behaviour could truly serve as an operational indicator of stress. We have now confirmed that," reports Tore S. Kristiansen, who headed the research project "Motivational states and coping ability as operational welfare indicators in farmed fish -- MORECARE."

The project, which received funding under the Research Council's HAVBRUK programme, is presented in the programme's latest newsletter ("Nytt fra HAVBRUK" no. 2/2010, available in Norwegian only).

Measuring the well-being of salmon and cod, however, is no simple matter. Fish express themselves differently from land animals -- it is not possible to judge the state of well-being of a salmon by its facial expressions.

Observing behavioural signs

"We measured the stress levels in salmon by how much cortisol they excreted into the water and by monitoring their oxygen consumption. Measuring cortisol in the water is expensive and time-consuming, so it's not feasible for producers. But the equipment and software used for quantifying oxygen consumption may be reasonably implemented into land-based aquaculture."

"For most producers, however, it's most practical to observe fish behaviour. Our research showed that following the fish behaviour -- either with video cameras or by trained persons observing -- could yield results just as good as those obtained by measuring cortisol or oxygen."

Blinking lights at feeding

In one aspect of the trials, researchers exposed the fish to a series of blinking lights half a minute before administering feed. This conditioned the fish to expect food after the lights appeared, which enabled observers to measure the strength of expectant behaviour and feeding motivation as the fish positioned themselves for feeding.

When the researchers stressed the fish by changing the tank-water temperature, for instance, or scrubbing the tank, they could then measure the stress reaction as behavioural changes in the fish. The duration of stress could be measured as well.

"Fish we did not expose to stress crowded together in the feeding area when they saw the blinking lights," explains Dr Kristiansen. "But fish that were anxious and stressed showed little or no expectant behaviour when they saw the lights."

Interpreting body language

Cameras and automatic photo analysis were used to quantify behaviour. This could open up possibilities for continuous monitoring of production fish in the future.

Both photo analysis and observation of fish body language may make it easier for animal technicians to interpret stress levels in fish. Personnel can tell whether or not the fish are stressed by observing differences in feeding behaviour, agitation in the form of rapid position changes, or fish crowding together at the floor or surface of the tank.