For adaptation to a water phase, prolactin is the required hormone, and for adaptation to the land phase, thyroxine.
fɔːɹ ˌædæptˈeɪʃən tʊ ɐ wˈɔːɾɚ fˈeɪz, pɹˈɑːlɐktˌɪn ɪz ðə ɹᵻkwˈaɪɚd hˈoːɹmoʊn, ænd fɔːɹ ˌædæptˈeɪʃən tə ðə lˈænd fˈeɪz, θˈaɪɹəksˌaɪn.