Exposure to a common herbicide can alter the minds of fish, researchers at the University of Otago have found. Atrazine, which is frequently used in New Zealand to kill weeds, was found at low levels in about three quarters of 36 streams and rivers sampled by another University of Otago study.
Low levels of atrazine in water doesn’t kill animals, according to research. But does the poison affect them in other ways?
To find out, master’s student Simon Lamb added atrazine to a tank of male zebrafish, the lab rats of the aquatic world, to a level frequently found in water sources in the United States.
Next, Lamb bred the males with female zebrafish from a non-atrazine tank. Then, he rated the parents and their offspring on a variety of behavioural tests.
“What most fish do when you put them in a new environment is they’ll settle down to the bottom, and then once they feel comfortable enough, they’ll swim up through the water column to the surface,” says Lamb.
By measuring how long it takes a fish to start exploring, behavioural researchers can get an idea of its anxiety levels and appetite for risk. Lamb also recorded how the fish responded to a mirror, which measures aggression. “We use these proxies to understand what sort of behavioural processes are going on.”
The zebrafish that had been exposed to the atrazine were less aggressive and had different risk-taking behaviour. The same was true for all their offspring—even though one parent hadn’t been affected by the chemical.
This has implications for whether atrazine should be used in New Zealand, says Sheri Johnson, Lamb’s supervisor. (Atrazine was banned in the European Union in 2004 due to high levels in groundwater.)
It’s not known how the fishes’ personality changes may affect their lives—will it alter their ability to find a mate, or to survive, or to evade predators? But the zebrafishes’ behaviour is thought to be widely indicative. “If we’re seeing these effects in zebrafish in the lab,” says Johnson, “that means we’re likely to see these same effects in our native fish in our rivers and streams as well.”