Fish or hen sits on it (5)

I believe the answer is:

perch

I'm a little stuck... Click here to teach me more about this clue!

'fish' is the definition.
(I know that perch is a type of fish)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for perch that I've seen before include "[SOMETHING FISHY]" , "bird comes down on" , "Freshwater fish - roost" , "Bird's seat - fish" , "Bird's roost" .)

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.