Fishermen are not required to report the fish that they catch. However, there are often strict regulations about how many fish of a certain species a person can catch in one day.
There are regulations around fishing in order to protect certain species from being over-fished. Fishermen should check to see what the legal fishing season in their state is, and whether specific species of fish are protected by law. If a ranger or other wildlife officer sees a fisherman disregarding these regulations, the fisherman can be charged with a crime. Catch and release fishermen are not subject to this, as the fish are not killed in the process.