Climb on a fish's back, perhaps? (5)
I believe the answer is:
scale
This clue might be a double definition.
'climb' is the first definition.
(scaling is a kind of climbing)
'fish's back perhaps?' is the second definition.
I know that 'fish' relates to this answer.
'on a' is the link.
Can you help me to learn more?
(Other definitions for scale that I've seen before include "Go up" , "Notes < magnitude" , "Alec's (anag) -- graduation" , "Doh, re, me etc" , "Tones rising maybe" .)