Fisheries science is all about understanding fish and their environment so that we can catch them in a way that is sustainable.
Imagine that you and your friends go fishing in a pond. You catch lots of fish, but if you keep catching them at that rate, there won't be any left for next time. Fisheries scientists study things like the number of fish in a particular area, the type of fish that live there, how quickly they grow and reproduce, and how many fish people catch.
They use this information to make sure that people can keep fishing in that area without hurting the fish population. They might tell fishermen to only catch a certain number of fish, or only catch fish of a certain size. They might even create rules about when and where people can fish, so that fish have time to grow and reproduce.
The goal of fisheries science is to make sure that fish populations stay healthy and that people can keep fishing for years and years to come.