There are about 28,000 living species of fish in the world. I found a story about the species discovered last year. Here's a link . It includes several kinds of species, including fish. They named one of the new fish after the mythical land of Wakanda from the Black Panther movie.

There may be many fish species that have not yet been discovered because it's so difficult to study what's going on in the ocean. One way is to drop nets deep into the ocean and look at what you find. Here's a story about new species they found this year (2020) that included fish that reflect almost no light.

Some fish at the bottom of the ocean give off light to signal others of their own species or to attract prey. Why do you think it would benefit a fish to not reflect any light?

There are about 28,000 species of bony fish and 1,000 species of cartilaginous fish that are known to science and that are alive today. There is some debate over whether the so-called jawless fishes are truly fish, but I was unable to find out how many species of them there are. I also haven't been able to find anybody counting up the number of extinct species of fish that have been discovered.

More species are found all the time, although generally in conditions that we haven't looked for them before, such as in the deep ocean, or in the fossil record (in the past, different species of fish lived in different parts of the world just as different species of fish live in different parts of the world today, so if most of our fossils come from North America and Europe, then traveling to another continent and collecting fish fossils will turn up not-yet-discovered species).

From Wikipedia : "Although most fish species have probably been discovered and described, about 250 new ones are still discovered every year. According to FishBase, 34,300 species of fish had been described as of September 2020"

From this site: "Researchers have discovered a new family of eel-like fish, named dragon snakeheads, which live in underground waters in southern India. These primitive fish are a type of “living fossil” and may have diverged from their nearest relatives more than a hundred million years ago. Oct 19, 2020"

Fish is a very diverse group with a total of 34 300 species described so far . FishBase is a website you can look up the information of the newly described species. They have yet to update the database for this year. However, you can find the 26 species described in 2019. Of those 26, there are fishes living in the coral reef, in the deep sea, in freshwater lakes. It is truly a testament of fish's diversity.