Thanks, science! Fish get depressed just like people

It turns out that not only can our gilled friends become depressed, but some scientists consider fish to be a promising animal model for developing anti-depressants. New research has been radically shifting the way that scientists think about fish cognition, building a case that pet and owner are not nearly as different as many assume.

“The neurochemistry is so similar that it’s scary,” said Julian Pittman, a professor at the Department of Biological and Environmental Sciences at Troy University in Alabama, where he is working to develop new medications to treat depression, with the help of tiny zebrafish. We tend to think of them as simple organisms, “but there is a lot we don’t give fish credit for.”

Dr. Pittman likes working with fish, in part, because they are so obvious about their depression. He can reliably test the effectiveness of antidepressants with something called the “novel tank test.” A zebrafish gets dropped in a new tank. If after five minutes it is hanging out in the lower half, it’s depressed.

If it’s swimming up top — its usual inclination when exploring a new environment — then it’s not. The severity of the depression, he says, can be measured by quantity of time at the top vs. the bottom.

(Pictured: In Dr. Pittman’s lab, researchers induce depression in a fish by keeping it drunk on ethanol for two weeks, then cutting off the supply, forcing it into withdrawal. This here is a depressed fish. Both clips, which represent a small segment of the five minute tank test, were extracted at comparable speeds. Credit: Troy University)
(Pictured: Give a depressed bottom lurker an effective antidepressant and within two weeks it will swim up top again. Credit: Troy University)

While scientists have used animals, like mice, to study emotional problems for decades, the relevance of those models to human experience is sketchy at best.

There’s the obvious issue that “We cannot ask animals how they feel,” says Dr. Diego A. Pizzagalli, the director of the Center For Depression, Anxiety and Stress Research at Harvard Medical School. Though researchers may find parallels in serotonin and dopamine fluctuations, neither fish nor rat can “capture the entire spectrum of depression as we know it,” says Dr. Pizzagalli.

There is a heated debate in the fish research community about whether anxious or depressed is a more appropriate term.

But what has convinced Dr. Pittman, and others, over the past ten years is watching the way the zebrafish lose interest in just about everything: food, toys, exploration — just like clinically depressed people.

“You can tell,” said Culum Brown, a behavioral biologist at Macquarie University in Sydney who has published more than 100 papers on fish cognition. “Depressed people are withdrawn. The same is true of fish.”

The trigger for most domestic fish depression is likely lack of stimulation, said Victoria Braithwaite, a professor of fisheries and biology at Penn State University, who studies fish intelligence and fish preferences.

Study after study shows how fish are defying aquatic stereotypes: some fish use tools, others can recognize individual faces.

“One of the things we’re finding that fish are naturally curious and seek novel things out,” said Dr. Braithwaite. In other words, your goldfish is probably bored. To help ward off depression, she urges introducing new objects to the tank or switching up the location of items.

Dr. Brown agrees, pointing to an experiment he conducted, that showed that if you leave a fish in an enriched, physically complex environment — meaning lot of plants to nibble on and cages to swim through — it decreases stress and increases brain growth.

The problem with small tanks is not just the lack of space for exploration, said Dr. Brown, but also the water quality tends to be unstable and there may not be sufficient oxygen.

“A goldfish bowl for example is the worst possible situation,” he said.

If you own fish, you might want to consider where Dr. Brown keeps his: an extensively-landscaped six-foot tank. He recommends a “two foot tank with lots of plants and stuff” for your average betta.

Source: The New York Times