I have worked for a university, the federal government, a tribe, a consulting firm, a state agency, and a city. In fisheries there are many job opportunities. I would suggest you study biology, chemistry, and math. Consider volunteering to gain knowledge and experience. Some volunteer opportunities may exist at aquariums, hatcheries, or in surveys done by agencies.
To become a marine biologist , it depends the collegue, but most of cases you have to study biology in general and the be study a post degree in marine biologist, because is a very specific field, but is such a good field , you can develop many skills and to be in the investigation field, in both animals and marine plants, and such other categories I imagine they may exist, also you may investigate by now where you can find the career, because the best ones are near the coast