One gliding right behind fish (6)
I believe the answer is:
skater
'one gliding' 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 within the answer.
'fish' could be 'skate' (skate is a kind of fish) and 'skate' is present 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 "Rink performer" , "Performer on ice" , "Dean, perhaps" , "Insect on pond - person on ice" , "Person sliding over ice" .)