Do fresh water fish contain more salt than marine water fish?

No,it is the other way round. Marine fish contains more than freshwater fish. That is because, what is available in media, very little of it will be found in the body of the biota contained in the media. read more

In contrast, body tissues in a freshwater fish contain more salt than the water in which it lives. As a result, water continually flows into the body of a freshwater fish through its skin and gills and the fish has no reason to take in additional water by drinking. read more

The streamlined shape minimizes energy expended to move through the water Most fresh water fish are hypertonic, meaning their body cells contain more salt than the surrounding water. read more