Fish Have Fear - understanding emotions through experiments on fish

Noorlinah Mohamed

July 07, 2014

By Assoc. Prof Suresh Jesuthasan

An addenda to his Brunch Talk at The O.P.E.N. on 28 June 2014

For millennia, philosophers, poets, writers, artists and scientists alike have puzzled over the complexities of human behaviour. Desire, anxiety, ecstasy, aggression and madness have long inspired both poetry and prose, music and lyric.

What would it mean for the sciences – and the arts – if we could definitively locate the source and cause of emotions like fear? The possibilities for further scientific exploration and literary extrapolation are endless.

To gain a better understanding of emotions and behaviour, scientists have observed humans, of course, and other animals as well.

In 1938, famed Austrian ethologist Karl von Frisch published his first report on a substance released through the skin of an injured European minnow: he called it 'Shreckstoff' – which translates literally into 'alarm substance' – and postulated that this substance caused fear in other fish. Indeed, the affected fish would dramatically change their swimming patterns - either darting away or freezing in place - in response to this 'Schrekstoff'.

Subsequent experiments by other scientists have confirmed that many freshwater fish display the same pattern of behaviour. The release of 'Schreckstoff' results in affected fish demonstrating all the classical hallmarks of fear, including physiological changes such as an increase in blood cortisol levels.

Associate Professor Suresh Jesuthasan and his team in Singapore's Institute of Molecular and Cell Biology have focused their research on the zebrafish – a tiny tropical fish whose brain activity is particularly easy to observe because of its optical transparency in its larval state. Although fish may seem different from humans, with an insignificantly small brain, many processes controlling emotional responses are similar.

In the process, they have partially cracked the mystery of what constitutes 'Schreckstoff'. Unexpectedly, one component of the 'fear' substance secreted by the zebrafish was found to be sugar molecules which break off when a fish suffers injury to its skin.

But how, you might ask, do the fish sense the alarm substance? Through calcium imaging, Jesuthasan's team have identified regions that were activated in the olfactory bulb of fish – indicating that fish actually do 'smell' danger in the water.

The greater the amount of the alarm substance, the higher the level of fear. This reflects a fundamental property of the brain, which is its ability to create a response that is optimal for any given situation. What makes this possible? Brain imaging has led the scientists to a obscure region of the brain, called the habenula.

Do we smell danger, as fish do? And do we give off pheromones that might alert others to the presence of something to be feared? In this talk, Professor Jesuthasan will discuss several aspects of fear, including what modifies the intensity of the emotion, and what brings it under control.

  • 2014