When swimming, plaice swallow gallons of ocean (7)

I believe the answer is:

pelagic

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

'when swimming plaice swallow gallons of ocean' is the definition.
I can't tell whether this definition defines the answer.

'when swimming plaice swallow gallons' is the wordplay.
'when swimming' indicates an anagram.
'swallow' indicates putting letters inside.
'gallons' becomes 'g'.
'plaice' is an anagram of 'pelaic'.
'pelaic' placed around 'g' is 'PELAGIC'.

Can you help me to learn more?

(Other definitions for pelagic that I've seen before include "Like an albatross" , "Inhabiting the deep" , "of the ocean" , "Marine" , "Sea" .)

I've seen this clue in The Guardian.

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.