I would add that exposure to the drug is only part of the story.  Unless everyone is flushing their meds, and depending on the medication in question, fish would be exposed to the metabolites of the drug rather than the drug in its original state.

Some medications pass through the human body effectively unchanged, while others are partially or fully broken down by the liver and other organs.  

No it doesn’t indicate that. At least not yet. While this is an interesting study, further research is needed, as the researchers are quick to point out.

Having worked in medical research, we’re almost always quick to say that more research is needed, and most media are quick to ignore that statement and jump to assumptions.

The researchers used, on purpose, a high dose of the medication to make sure that they got a reaction. They admit that the dose does not reflect what is found in most natural environments, and that wasn’t their point to begin with. They got a reaction, and now the want to do more research to see if they can get the same results at the lower dosages found in more natural environments.

As of yet, there is not enough research to support your statement. Indeed, that statement is at the heart of the question they’re asking.