The turbine blades of marine renewable energy devices pose a striking/collision risk to marine species. Consequently, where a proposed site contains a major fishery, there can be conflicts with local fishermen and stakeholders. Meanwhile, the striking/collision risk is considered low based on data from tidal power generation test sites. There are some unknown aspects due to a lack of observational data, in particular, the data that indicates direct striking. Therefore, this paper attempts to show an example how fishes strike turbine blades even though the rotating blades are slower than fish swimming speed. A preliminary experiment was carried out in a laboratory-scale water tank using the fish Gnathopogon elongatus. The fish is distorted by the current and sometimes distracts the rotating turbine blades. Thus, the fish had a high risk of striking the turbine on several occasions, suggesting that they may strike the turbine if they lose their cautiousness of it. The experiment showed that fishes such as Gnathopogon elongatus, which can be considered abnormal in some situations, may have an approximately 1% chance of striking turbine blades in the water tank test although they would have the ability to avoid the slow rotating turbine blades under the normal situation.