Answers (1)
Fish are a group of a great number of different families, I believe the number of families is in the hundreds, and the number of individual species to be close to 30 000. All of these families make up a large number of different orders, that in turn makes up several classes.
The taxonomic rank you are referring to might be what is called the phylum - the rank below kingdom and above class. For fish, that would be the chordate. Cheers!