Bad news for pescatarians: A new study shows that the common belief that fish aren’t sentient creatures may be unfounded.

Thanks to their tiny little brains and lack of cerebral cortex, fish are often seen as stupid, emotionless creatures. But recent research suggests it’s not that simple. Studies have found that fish can do quite a lot with their small brains, including use tools, navigate waters, and recognize social rank.

Now, a new study published in Proceedings of the Royal Society B finds that fish might have emotions, too. Scientists from the Institute of Aquaculture found that zebrafish responded to stress with what is known as an “emotional fever,” or a rise in body temperature.

The researchers used six groups of zebrafish in the study. They placed them in tanks divided by plexiglass into six chambers, each containing water of a different temperature. The chambers were still interconnected so that the fish could swim between them.

The scientists allowed the fish to acclimatize to the water overnight. Next, they confined three groups of fish using a small net, thereby inducing stress. Afterwards, they released the fish into the central chamber and tracked their movements. The researchers found that the confined groups swam to the chambers containing warmer waters, but the unconfined groups stayed where they were. By going into warmer water, the stressed fish raised their body temperatures a full 1-2 degrees.

The study’s conclusion: The change in temperature preference and subsequent rise in body temperatures means the fish were demonstrating emotional fever.

“This finding,” they write, “removes a key argument for lack of consciousness in fishes.”