That bottom image is not bad, there is only the effect of it being taken through glass,Taken on a Panasonic Lumix (manual setting). 1/50s @ f4.2 ISO 800
The bottom image is untouched, the top one has been cropped and levels adjusted.
View attachment 449580View attachment 449581
Most decent smart phones have manual settings, so have a play around. As has been said, turn off the flash and get as close to the glass as posible. Also shoot straight through the glass. not at an angle as the average zoo aquariun glass is many mm's thick which will distort the image and make the auto focus do funny things.
I'd be happy with that image, just needing to use minimal editing