A person who specializes in fish is called an ichthyologist. Ichthyology is the branch of Biology devoted to the study of fish, their habitats, behaviors, and physiology. Ichthyologists often work in research, conservation, and fisheries management to better understand and protect aquatic ecosystems.
Hepatologist
It is a person who specialises in cooking fish only.
Pediatrician
Geriatrician
A radiologist is a person who specialises in diagnosing and treating diseases using medical imaging techniques -X Rays included
stein
fishmonger
I'm thinking of farmer or horticulturist?
A Percussionist. "Tambourinist" is also a valid term for someone who specialises in the tambourine.
Pescatarian
a person who specialises in medical language.
You call that type of person an solitarian.Hope that i helped!!!