What is the study of fish called?

 Ichthyology

Explanation:

• Ichthyology: The branch of zoology devoted to the study of fish, including bony fish (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). The term is derived from the Greek words "ichthys," meaning "fish," and "logia," meaning "study."
• Herpetology: The branch of zoology concerned with the study of amphibians and reptiles.
• Ornithology: The branch of zoology that deals with the study of birds.
• Saurology: A sub-discipline of herpetology focusing specifically on the study of lizards.

Therefore, the study of fish is called Ichthyology.