Can fish live in freshwater an live in saltwater?
The lake sturgeon is often called a "living fossil," part of a family of fish that has existed for more than 135 million years.
here is some picture of fish can live in both water and facts for that fish.
The smelt is distinguishable from all other fish common in our waters by its slender form, combined with a long pointed head, large mouth, a small but evident adipose fin standing above the rear part of the anal, and a deeply forked tail.
Despite having been known for hundreds of years, the American eel (Anguilla rostrata) has a complex life history which, even today, is not fully understood
so there is fish can live in both water. but there is fish can't live in both water.