Helping Aubie this week is Dr. Carol Johnston, a professor of fisheries at AU.

Dear Brandy,

The number of fish species in the ocean is actually a complicated, and very interesting question! The number of fish species is continually rising, as more and more species of fishes are discovered each year. Believe it or not, we still haven't discovered all the fishes in the ocean, or in freshwater either. Fishes are generally either marine (living in saltwater, like the ocean), or freshwater, but rarely both. This is because it is difficult for fishes to regulate the amount of ions in their bodies, and they either have
mechanisms for pumping them out (marine environment) or keeping them in (freshwater environment). There are about 25,000 species of fishes known from both marine and freshwater environments. A little over half, or 58% live in the ocean. What's remarkable is that most of the rest, 41%, live in freshwater, although there is very little freshwater habitat relative to marine. Freshwater habitats tend to be more isolated, which has produced more species over time.

Thanks for your question!

Aubie and Dr. Johnston