In need of cracking fish in desperate need (7)
I believe the answer is:
encoded
'in need of cracking' is the definition.
(something in code must be cracked)
'fish in desperate need' is the wordplay.
'fish' becomes 'cod' (type of fish).
'in' indicates putting letters inside.
'desperate' indicates an anagram (a desperate or pathetic spelling).
'need' anagrammed gives 'ened'.
'cod' going inside 'ened' is 'ENCODED'.
(Other definitions for encoded that I've seen before include "as secrets are dispatched?" , "In cryptic version" , "formed in a difficult-to-understand way" , "Deed con (anag.)" .)