If it wasn't clear before, it certainly was during Jesus' last moments with them before he ascended into heaven, because he tasked them with becoming evangelists; to share the good news of the New Covenant. It finally sunk in why they were called to be fishers of men.
You ever wonder why the analogy of fishing came into play? Well, there might be more to it than what we originally thought. Here are some things to think about:
1) A good fisherman knows what bait to use, and it varies. He has to understand how a fish thinks. He must know what interest the fish he's after because not all fish are the same. This is comparable to when we're trying to lead others to Christ. We must meet them where they are and understand their needs. We must provide them with the bait they need.
2) A good fisherman knows you can't just yank the fish up or you'll more than likely lose it either slipping from the hook or breaking the line. People don't like to be jerked around or you'll lose them. Playing hardball with most people isn't a good move.
3) A good fisherman knows the breaking point of his or her line. If you've fished enough, you can actually feel when you're close to pushing it too far. It's during those times when a fisherman adds slack to the line and lets the fish feel safe again before trying to time it right and give it another try. What this boils down to is patience and guess what, it's a godly virtue.
Let's make God proud and do what he's commissioned us to do, and that is to share the good news, and to become ourselves, fishers of men.