Mutation 1: Gills become stiffened like in Mudskippers so they do not stick together when coming out of water, and it helps to trap some air within them when out of water, thus increasing air breathing time.
Mutation 2: Have a second version of Hemoglobin called Cathodic Hemoglobin like in Hoplosternum littorale, where the oxygen affinity increases with decreasing pH, in order to ensure sufficient oxygen to tissue under low oxygen and acidic conditions.