Question

why does fish can't breathe outside of the pond..

Answer 1

When fishes are taken out of water, their gills collapse and there is no enough  surface area for diffusion to take place.

Hope it helps

Answer 2

because fishes used gills to breathe in water .however humans use lungs to breathe in land. fishes don't contain lungs. thus they cannot breathe out side the water

hope it helped u