Bones one found attached to fish (5)
I believe the answer is:
carpi
'bones' is the definition.
(I've seen this before)
'one found attached to fish' is the wordplay.
'one found' becomes 'i' (I am not sure about this - if you are sure you should believe this answer much more).
'attached to' means one lot of letters go next to another.
'fish' becomes 'carp' (carp is a kind of fish).
'i' put after 'carp' is 'CARPI'.
Can you help me to learn more?
(Another definition for carpi that I've seen is " Wrist bones - Capri (anag)".)