Hi,
What I recommend for any career is that you contact someone who has the job you want. Tell the person that you are a high school senior exploring careers and ask if you can interview them. Ask the person the best and worst parts of the job, the general pay scale (not what they make specifically, because that’s personal), the formal training required, and the non-formal skills that help to get a job in the field (foreign language experience, GIS work, ability to operate vehicles, etc.). Ask about the best schools and programs. Ask whether there are many jobs available and how you can be a good candidate.

A lot of people think they are interested in marine biology or working with vets because they love animals or think dolphins are cool. You will want to demonstrate that you are really serious about the career. If possible, find volunteer opportunities, even if they are not exactly in line with your career. For example, if you have a good record of volunteering at a local animal shelter, doing the “dirty work” of animal care, a potential employer will know that you understand the realities of the job and don’t just picture yourself “high-fiving” Flipper.

Once you identify some possible programs, ask your high school guidance counselor to help you make sure that the programs are accredited. He or she will know what that means.

Most people change their careers more than once. What does a marine vet tech do every day? You may want to look at some vet tech blogs to see what an average day is like if you aren’t sure. Think about what kinds of things draw you to that career. What kinds of things will be the worst part of the job? Your guidance counselor can also help you think about these things and other career options that you might even like better.

Veterinary programs in undergrad institutions are generally focused on going toward veterinary school, which is a type of graduate school. Their purpose is to prepare you for standard veterinary medicine which probably isn't what you want to do. For marine animals, you are going to need to find an employer who needs to take care of marine animals, and this means a much more limited number of jobs and a much more focused area of expertise - most probably, you are looking at either working in an aquarium, or at a water-focused amusement park like Sea World.

I would recommend you look at or contact aquaria or ocean parks for what kind of training their staff require. The Monterrey Bay Aquarium would probably be a good place to start asking around - they are always interested in public education and would be eager to talk to you. My guess is that you're looking at getting a degree in marine biology. Schools with good marine biology programs that you might want to check out include (in no particular order) UC Santa Cruz, UC Santa Barbara, and UC San Diego, but check with the aquarium first as to what they need.