What filter to use to take pictures

why do you think you need a filter? What are you trying to achieve that you think you need a filter for?

If anything I can think of it would be a Polarizer to get rid of any glare but it will cost you speed. With moving fish that's not ideal as you'll want the fastest shutter speed you can get.
 
No, shoot in RAW and adjust the White Balance in software in post processing.
 
you can use a yellow filter but that's old school :). Jesse has it spot on, RAW is all you need! All the color correction you could want at the tips of your fingers - via the keyboard :).
 
Back
Top