THEY FEEL

It’s hard to tell if a fish is suffering. They make no sounds and have no facial expressions. But scientists have begun to work out other ways of gauging their mental state. Zebrafish, the lab rats of the fish world, have been shown to suffer from emotional stress. When trapped in a small net, a zebrafish’s body temperature rises by several degrees. Known as emotional fever, this involves the body responding to stress in the same way it does following infection by a pathogen. It was previously thought that only humans suffered from stress like this.

The finding adds to mounting evidence that fish detect and feel pain, even though they lack a neocortex, which is the mammalian brain region responsible for pain perception. Following findings like these, standards for the ethical treatment of fish are gradually catching up to those for other animals. In Britain it’s illegal to mistreat pet fish (recently a man was convicted of cruelty to animals when he allegedly swallowed a live goldfish) and in Germany recreational fishermen must keep, humanely kill and eat any fish they catch, without releasing them again, otherwise their sport is deemed to cause unnecessary suffering.