if you can try increasing the shutter speed this will reduce the blurry ness of the fish, and be as stable as you can as you follow them through the view finder, I'm no expert with cameras so bare with me if this next part is wrong, but increasing shutter speed my reduce the brightness of the picture so u may also need to increase? aperture which should allow more colour into the picture also try without the flash i love photography and for me its one of the hardest things through glass/water so i haft to congratulate you on those pictures they are stunning