well first of all its because the different fish that you have put to the alarm... have probably passed down some mutations that allow them to change to their environment more quicker and some of them just don't have mutations which is probably why they don't show any change. same with cockroaches if you have 1,000 cockroaches and you use raid those that you sprayed would probably be dead but out of those 1,000 only 20 survived since they have a mutation in their genes, so they will reproduce and by end of the month there will be 1,000 more cockroaches! hope this helps
