Personally, I'd recommend holding off on calling yourself "an ichthyologist/marine biologist" unless you have a degree, or perhaps are in some sort of very special program for 16-year-old "scientists." At the very least, I would expect you to work during the summer at Sea World.
Being very interested in something is enough credibility for now, studying to be something is just fine. But you never know when a professional ichthyologist might be reading the board, and take offense.