I find if you put the mirror or another male behind the fish you want to photograph then they will sit still in full flare and perfectly lined up with the camera for you. Like thisAny tips on getting a fish to slow down and stop wiggling all over the place while he's flaring? Morpho refuses to hold still long enough for my Droid Turbo to get a good zoomed in shot of him flaring. He also somehow manages to get his tail folded over sometime between when I tell the phone to shoot and when the photo gets taken.
Or if he flares at a stick or something he might give you the side on, still flare aswell
And yeah sports mode or anything with high shutter helps a lot too