There’s no happy ending for shrimp exposed to the mood-booster Prozac, according to a new study.

Remnants of antidepressant drugs flushed into waterways worldwide are altering shrimp behavior and making them easier prey, experts say.

To mimic conditions in the wild, scientists exposed the estuary-dwelling shrimp Echinogammarus marinus to the antidepressant fluoxetine at levels detected in average sewage-treatment waste. Fluoxetine is the key ingredient in the drugs Prozac and Sarafem.

Shrimp normally gravitate toward safe, dark corners. But when exposed to fluoxetine, the animals were five times more likely to swim toward a bright region of water, the team discovered.

"This behavior makes them much more likely to be eaten by a predator, such as a fish or bird," said study co-author Alex Ford, a biologist at U.K.’s University of Portsmouth.