Fish on river or one on ice, perhaps (6)
I believe the answer is:
'ice perhaps' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'fish on river or one' is the wordplay.
I cannot quite understand how this works, but
'fish' could be 'skate' (skate is a kind of fish) and 'skate' is located in the answer.
'river' could be 'r' (abbreviation for river) and 'r' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'on' acts as a link.
Can you help me to learn more?
(Other definitions for skater that I've seen before include "Could one roll up" , "Athlete on blades" , "Winter sportsman" , "Streak (anag)" , "One sliding over ice" .)