One going over ice right behind fish (6)
I believe the answer is:
skater
'one going over ice' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'right behind fish' is the wordplay.
I cannot really see how this works, but
'right' could be 'r' (abbreviation) and 'r' is present in the answer.
'fish' could be 'skate' (skate is a kind of fish) and 'skate' is located in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for skater that I've seen before include "Winter sportsman" , "Performer on ice" , "One on blades/wheels" , "Could one roll up" , "One sliding over ice" .)