Question

give reasons for we cannot survive in water whereas a fish can.

Answer 1

A fish breath through it gills in water but we don't have gills to breath in water.
As the gills of fish provide itself oxygen from water but our lungs and nose are not able to do so.

Answer 2

We can't survive in water because we don't have gills like a fish . We don't have organs like them. If we'll go inside water we can only survive for 20 -25 seconds .So that is we can't survive in water