* Ongoing Discoveries: Scientists are constantly discovering new species, especially in remote areas.
* Changing Classifications: The way we classify species is constantly evolving, leading to changes in the number of recognized species.
* Difficult to Define "Freshwater": Some fish may spend part of their lives in freshwater and part in saltwater, making their classification tricky.
However, estimates generally range between:
* 10,000 and 15,000 species
This is a significant number, and it emphasizes the vast biodiversity of freshwater ecosystems around the world.