Fish are predators and will check out anything new in their environment as it may be a source of food; or could be a threat to their safety. Fish have curiosity, and they also have memory to be able to remember what they learned. Enough repetitions of the laser without the reward of food for checking it out and the fish will learn to ignore the laser. BUT it takes thousands of repetitions; they do not learn fast and their instinct to check out everything for food or threat is extremely strong. Evolutionary imperative, it is called.
Question. Do you know if the fish chased the laser if it was moved?