Diversity Fish have been around since before the dinosaurs. There are more kinds of fish than there are amphibians, reptiles, birds and mammals combined (about 25,000 species identified so far). Of these, nearly 10% are species of catfish. Even though only a tiny fraction of one percent of the planet’s water is found in lakes, rivers, ponds, and streams, over 40% of fish species live in freshwater, not the ocean. The ocean has many more individual fish, but more diversity is found in freshwater. Over 1,100 fish species are threatened with extinction, most of these in freshwater. The Hudson River and its watershed have 216 species of fish (and counting).