A zoologist.
An ecologist studies pollution
A mineralogist studies minerals.
Ichthyology is the branch of zoology devoted to the study of fish.
The kind of scientist who studies Urology would be a Biologist, since Urology concerns a biological function (urination). If you mean the kind of doctor who studies Urology, that would be a Urologist.
meteoroligists
Audiologist
An Ichthyologist.
Botanist
seismologist
a biologist
cosmologists
Mathmaticion