Well, biology and chemistry of course. It's always a bonus to take physics. Some sort of math as well.
I think once you get into high school it's extremely important to do some volunteering relating to fish.. If you have any sort of local aquarium that'd be excellent if they'd let you do anything. Once you reach grade 11/12 our high school organizes co-ops for us where you can get direct experience working in the field you want.
Surround yourself with fish via volunteer and as Olympia said, science-y courses will help you transition into university level courses. We have an entire water studies campus here called the Marine Institute. I'm providing a link to the courses they offer just as basic for you to investigate. As you can see, the academic area of fish is not limited!! Good luck! http://www.mi.mun.ca/programs/
Maybe you could read up and challenge yourself to write your own biological field study. Ask yourself a question, gather data and hypothesis and go to a local waterworks and test out your hypothesis! Keep the data and everything you record. It can be a good hobby which keeps you motivated and interested, while also providing references for a portfolio if you ever need one.
You don't necessarily need to be present with other scientists in order to conduct research. I don't know how close a university is to you, but ask around and see if some profs are open to running a public information session.
Do you have a nearby water system? Like a tiny creek or something?
I'd get a spare tank, anything 1 gallon up. Collect some soil from the water and water insects. 10 gallons plus and you can add some minnows in as well. You can observe how the species interact. The great thing about this is that the tank will be 100% "cycled" due to tons of life in the soil. Not too scientific, yes.. I'd get some fish books that you understand.. Read and read and you can start moving onto more complex literature (you may know more than people your age by then- I took biology this year and everything but genetics was stuff I pretty much knew by heart- got a 95 in that class!)
Insects may not seem fish related but remember that everything is connected- you will have to know about fish the most, but you will need to know a lot about all other aquatic life as well. Posted via Mobile Device
Experiment with lots of different styles of tank and eco-system, as well as different fish species. Do you have an aquarium near you, or a zoo with an aquarium section? One of my friends volunteers there as a fish feeder. It means she gets to feed giant groupers and cave nurse sharks.
Read lots, about both fresh and saltwater species. As well as the courses Olympia has mentioned, do keep up with English as well. Employers are always more impressed with excellent spoken and written skills, and as ichthyology will no doubt land you in a research position, it will stand you in good stead for writing papers and reports.
Laki: I will fit that into the summer and start a journal thread to record my results(also a real journal like the scientists).
Bombalurina: The closest zoo has only feeder fish for the other animals(the next closet zoo is two hours away).