How many letters does the top answer for “a zoologist who studies fishes” have?

The most common answer is ichthyologist (13 letters).

Crossword clue: a zoologist who studies fishes

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

ichthyologist 13 letters wn-def

a zoologist who studies fishes

a zoologist who studies birds 50% similar → ornithologist

a zoologist who studies insects 50% similar → entomologist

a zoologist who studies protozoans 50% similar → protozoologist