Answer
Some other species may have adapted to detect the alarm substance for either defense or predation. Some other species may not have this adaptation, or may not change their activity even if they do detect it.
Work Step by Step
Animals often adapt to take clues for other species that live in the same environment as them. The alarm substance could alert some fish that they were in danger, which would lead to behavior similar to the minnows.
Not all other fish would have this adaptation, though, and some that did may not change their behavior from this signal alone.
