A study published by the Society of Environmental Toxicology and Chemistry in Portland, Oregon, reveal that even the smallest amount of chemicals we flush out from our house alter the mating and breeding behavior of the fishes.

These subtle behavioral effects, unlike physiological and anatomical effects, are difficult to trace.

"Subtle effects are the issue," says Melissa Schultz, a chemist at the College of Wooster in Ohio. "It's easy to tell if a fish suffers from obvious anatomical changes such as being intersex or not having mature secondary sexual characteristics," she says. It requires more meticulous work to determine the effects on mating behavior.

Two different studies by Dalma Martinović, an environmental toxicologist from the University of St Thomas in St Paul, Minnesota, and Melissa Schultz show that even a lowest concentration (0.01-0.5 micrograms/liter) of chemicals can cause significant reproductive behavior changes in fishes.

Fishes which usually protect their nests in the wild failed to do so and their courtships behavior changed considerably when exposed to low levels of triclosan and Ibuprofen, a chemical found in anti-bacterial drugs.

“Physiological endpoints are less sensitive than behavioral ones," Melissa says. "I think effects on behavior might be more common than we realize. We are finding subtle effects at environmentally relevant concentrations.”

Scientists are concerned that these behavioral changes can even wipe out the fish species from earth. "We need to be paying more attention to behavior, especially with pharmaceuticals,” says James Lazorchak, an aquatic biologist from the US Environmental Protection Agency in Cincinnati, Ohio.