Swimmer in biker gear? (13)
I believe the answer is:
leatherjacket
'swimmer' is the definition.
(leatherjacket is a kind of fish)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for leatherjacket that I've seen before include "Cranefly larva" , "Hold close" , "Tropical fish -- heckler at a jet (anag)" , "Swimmer" , "Cranefly grub" .)