Why do sea animals need salt water?
Hermit crabs need salt water in their tank because they have an exoskeleton (they molt), and to keep it hard they need to just walk through some SEA salt water. They need SEA salt because table salt will blister their modified gills and will sofacate them. They need DISTILLED water because the clorine in tap water will do the same to their gills(they can still drown though) I have salt water in my hermies tank…
Some animals that live primarily in saltwater need fresh water because saltwater does not absorb the necessary impurities from their metabolic systems. Salmon and some species of eels spend part of their life cycle in fresh water (where they have to retain salt) and part in the sea (where they have to balance their body salt with the saltwater around them).