Can I use “fishes”?

Of course you can, if you refer to:

  1. A scientist, who studies fish (ichthyologists), for example, often refer to different species as fishes.
  2. To the Bible, as Jesus fed thousands of people with loaves and fishes.
  3. The movie The Godfather popularized the saying that someone sleeps with the fishes to indicate that he or she has been killed by the mob and dumped in the water.
  4. A few different sayings that begin with If wishes were fishes.