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 quite understand how this works, but
'right' could be 'r' (common abbreviation) and 'r' is found in the answer.
'fish' could be 'skate' (skate is a kind of fish) and 'skate' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
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" .)