With more than 15,000 species, nearly a quarter of the total number of vertebrate species on Earth, freshwater fishes are extremely varied. They include the largest fish species, the beluga at over 7 meters long, and the smallest, the Paedocypris at just 8 millimeters, as well as the carnivorous, such as the piranha, and the calm, such as the Chinese algae eater. Certain species evolve rapidly, cichlids for example, while others transform very slowly, like lungfish. The fossi