Without looking at your capX im guessing that you would compare the tap position to the fish.X position and then mirror the Fish if required to based on the side of screen tapped on relative to the fish of course.
if fish is on left side(tap.x>fish.X) of tap position set mirrored
if fish is on right side(tap.x<fish.X) of tap position set not mirrored
if you needed to you could spawn an invisible sprite at the tap position to help determine x position compared to the fish sprite x position.
Does that make sense?