I used to be able to bring fish onto my flights as carry-on so long as they were in a handled case. Since the airlines are getting tougher on what is allowed to be brought on, I've had my recent attempts to bring fish on my flights stopped in both carry-on and checked luggage.
Your best bet is to ship them air cargo before heading for your flight. The rates are cheaper airport to airport. Just try to have your fish arrive around the same time as your destination arrival time. Be aware that some cargo offices close at 5PM. So, try to schedule your arrival time to provide for sufficient time to pick up your luggage, get to your vehicle, and get to the cargo office before they close.