In contemporary science education, the trend is to engage students in hands-on activities in which they must manipulate equipment and gather data in an effort to answer questions. Hands-on experiences may turn out to be meaningless unless the experiences are well designed, planned, and focused so that students are guided to construct accurate mental constructions. A superior approach is to engage students in activities in which variables are controlled and general research procedures are used. In this article, the authors present a science activity that will help students understand how fish species find and identify each other--a potentially critical element in their survival when a predator-prey relationship exists between two species. The activity involves a real-world problem that the authors believe is a good tool both to motivate students (Roth 1991) and to engage them in research. Students are required to collect and organize data on two fish species, examine the data mathematically, draw conclusions about the organisms with which they work, and extrapolate to other environments. (Contains 3 figures and 2 tables.)