Fish bones across middle of jetty (8)
I believe the answer is:
sturgeon
'fish' is the definition.
(type of fish)
'bones across middle of jetty' is the wordplay.
'bones' becomes 'surgeon' (I can't justify this - if you can you should believe this answer much more).
'across' is an insertion indicator.
'middle of' says to take the centre.
The centre of 'jetty' is 't'.
'surgeon' going around 't' is 'STURGEON'.
Can you help me to learn more?
(Other definitions for sturgeon that I've seen before include "Fish - got nurse (anag)" , "Caviar supplier" , "swimmer" , "Fish that yields caviare" , "So urgent to find caviare-bearing fish" .)