Well, I'm guessing you've caught one by now! If not, use the lure located at the very top of your tacklebox. Look for a large shadow in the water, and cast right at it. If done correctly, you'll get a "perfect cast" which automatically "hooks" the fish. You will still have quite the battle reeling the big guy in though. If that doesn't work, then cast the same lure and follow the onscreen prompts to create the necessary "action" required to attract the fish. A Titan should hit it sooner or later. The largest one I caught was a little over 103 pounds.
As far as other unique fish go, use the same strategy regarding perfect casting. When highlighted in your tacklebox, each lure displays pictures of which fish are drawn to it. If you are trying to angle a fish using the wrong lure, it will likely never happen.