Source : Webster's Revised Unabridged Dictionary (1913)

Ichthyology \Ich`thy*ol"o*gy\, n. [Gr. ?, ?, a fish + -logy: cf.
   F. ichthyologie.]
   The natural history of fishes; that branch of zo["o]logy
   which relates to fishes, including their structure,
   classification, and habits.

Source : WordNet®

ichthyology
     n : the branch of zoology that studies fishes