Two bodies of water both short of fish (6)
I believe the answer is:
tarpon
'fish' is the definition.
(tarpon is a kind of fish)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tarpon that I've seen before include "Great fish of Florida" , "No part for this large fish" , "Large silvery game fish of coastal waters off Florida" .)