The pumpkinseed sunfish, an invasive alien species, is found in nature reserve "De drie vennen". The fish threatens to devour the entire population of the native spadefoot toad. In three subsequent short games, the pupil / student will investigate what to do about the pumpkinseed sunfish. The first two are ecological simulations, in which the student carries out scientific ecological research (i.e. formulating a hypothesis, carrying out an investigation, interpretating the results in the light of the hypothesis). These two together take one school hour. The third is a game in which the students work in teams of five. Each team challenges the other teams in combatting the pumpkinseed sunfish in the most effective and most economic way.