They have about the same salt concentration as we do - not like the ocean. Four fins for steering - the precursor to arms and legs. There are more species and strange types than all other vertebrates put together. A gas bladder containing oxygen evolved for control of density that evolved into lungs for amphibians. Number of gill arches reduced and operculum helps pump water through the gills.
Some fish still filter feed.
Amphibians have no scales, limbs are developed for purchase against the earth, respire considerable through wet skin, only in fresh water, eggs require water to develop, external fertilization of eggs. Reptiles have eggs that do not need water to develop, have tough skin that cuts water evaporation, legs positioned for faster movement, better blood circulation pattern, internal fertilization of eggs. Better developed brain. Shorter Neanderthals were found in Europe - we can get some DNA, which shows that they may not have been our direct ancestors. They dissappeared whrn modern man appeared.