Fish could be present after leaving port (3)
I believe the answer is:
ray
'fish' is the definition.
(ray is a kind of fish)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for ray that I've seen before include "Shaft of light" , "Man who engaged in surrealist photography" , "Shaft, beam" , "Flash < Movie Player" , "Beam; flat-bodied fish" .)