Fish are typically viewed as simple organisms that don’t think and just go off of instinct because of their small brains, but a study published in November of 2015 suggests that zebrafish may be conscious beings that are aware of their own suffering. The researchers went off of other recent studies that discovered that the dorsomedial and dorsolateral telencephalic pallium in the forebrain of fish are functionally the same as the amygdala and hippocampus in mammal brains, which are responsible for emotional responses to stimuli. There are physiological changes in mammals when they experience emotions so the researchers measured physiological changes in the fish when they were put under stress to see if happened in them as well. Stress-induced hyperthermia (SIH) is shown in mammals and birds when they are under stressful situations, so the researchers wanted to see if zebrafish showed SIH when put in a stressful environment. SIH is thought to be a survival adaptation for fish because stressors can be precursors to a life-threatening event so increasing their body temperature can increase their chances for survival. Evidence of SIH would mean that the fish have a physiological response to a stressor, indicating that they are conscious beings and have an emotional response to stressful situations.
They divided a fish tank into 6 sections with Plexiglas with a hole in it so the fish could switch from section to section and kept each section at a different temperature. The temperatures were 17.92, 24.83, 26.92, 28.75, 32 and 35˚C. The ideal temperature for the zebrafish was 28˚C. To get rid of confounding factors, the oxygen levels in all the chambers were kept high and equal to each other. They studied 6 groups that had 12 fish in them. All of the fish were put into chamber 4, the ideal temperature chamber. But 3 of the 6 groups were experimental groups and were confined in a small fishing net in the chamber for 15 minutes before being released. Being confined in a fishing net is a known stressor for zebrafish. Every 30 minutes for the next 8 hours, the sections of the tank that the fish chose to stay in were recorded.
The results showed that...
- For the first 4 hours after confinement, the stressed zebrafish had a greater percentage in sections above 28˚C than the control fish
- After 4 hours, the stressed zebrafish slowly started to migrate back to the 28˚C chamber
The graph shows the chamber preferences for the control fish in blue and the confinement fish in red for the first 4 hours after being kept in the net. The confinement fish showed a greater preference for the warmer chambers than the control fish.
Their results showed that the stressor of being confined changes the water temperature choices of the zebrafish because the confined fish spent more time in the warmer water which raised their body temperatures by 2-4˚C. This measurable change in behavior and body temperatures of the confined fish is evidence of SIH which led researchers to conclude that fish have emotional responses to stressful stimuli, an indicator (but not proof) that fish are conscious beings. The zebrafish that were confined showed a change in behavior for 4 to 8 hours after the 15 minute confinement stressor, showing that brief stressors can have an impact on the behavior of zebrafish long after the stressor is removed. Based off of their data, they also concluded that the water temperature that fish prefer can be an indicator of their health because the stressed fish chose to be in warmer chambers than the non-stressed fish chose to be in.
So next time you’re tormenting your beta fish in your dorm by tapping on the glass or trying to catch your goldfish in a net, keep in mind that it may be emotionally impacted and you could be inducing SIH in your fishy little friend.