Fish at a popular aquarium in Australia have begun to show signs of depression after the facility was closed to the public in mid-March due to the COVID-19 pandemic.
According to marine biologists on staff at Cairns Aquarium in Queensland, Australia, a number of fish became lethargic and disinterested in their environment without human visitors to engage with through the glass.
Others decided to hide in dark corners of their tanks, and one fish in particular, a Queensland grouper named Chang, stopped eating for several weeks.
'A lot of people don't realize that animals can see outside of the tank and see the people, they actually really enjoy the human interaction,' Paul Barnes, a curator and marine biologist at Cairns, told ABC News.
According to Barnes, fish are curious animals and appreciate having new things to look at and explore, both in their tanks and outside of them.
'Just people going past the exhibits is a form of stimulation for these animals,' Barnes said.
'They like watching faces, the different colors people wear.'
To help the fish deal with their depression, aquarium management decided to hire an additional diver to swim with them and keep them company.
'We've got these leopard sharks, and they almost like being held or cuddled like puppy dogs,' Daniel Leipnik, Cairns' chief executive, told AAP.
'We normally have two divers, we now have three. So there's a bit more human contact going on, just to create that extra stimulation.'
Fish are so sensitive in part because of how closely their neurochemistry resembles a human's - 'so similar it's scary,' Troy University's Julian Pittman told the New York Times in 2017.
The depressive feelings are likely due to fluctuations in serotonin and dopamine similar to what humans when they're depressed.
Pittman even uses fish to test the effective of antidepressant medications, which he says he can measure by how active a fish is in the tank.
If the medication is effective, the fish will swim to the top of the tank and begin exploring, sometimes within a matter of a few minutes, but when the medication doesn't work, the fish will remain almost motionless in a bottom corner.