Subject: Will small amounts of anti-depressant drugs change the behavior of fish?

  I recently read an article that sparked an idea for my science fair 
project this year.  This article said that certain anti-depressant drugs 
that people are taking can pass through the people's systems, go through 
the wastewater treatment plant, and still enter our water, biologically 
active.  Even though these drugs are in such minute amounts that a 
difference may not be recognizable, they are still biologically active, 
and could perhaps harm plants & animals.  My idea:  to take two tanks of 
fish, having one as a control, and having small amounts of anti-depressant 
drugs in the water of the other tank, seeing if it makes a difference in 
the fish.  
  My problem:  How can I measure the difference in the behavior of the 
fish?  Would it be better to go with physical evidence, such as comparing 
the weight of the fish after a short period of time?

Re: Will small amounts of anti-depressant drugs change the behavior of fish?