Fish no guest relished at first unfortunately (8)
I believe the answer is:
sturgeon
'fish' is the definition.
(type of fish)
'no guest relished at first unfortunately' is the wordplay.
'at first' suggests taking the first letters.
'unfortunately' indicates an anagram (a bad or unfortunate spelling).
The first letter of 'relished' is 'r'.
'no'+'guest'+'r'='noguestr'
'noguestr' anagrammed gives 'STURGEON'.
(Other definitions for sturgeon that I've seen before include "caviar suppliers" , "Source of caviar" , "Shark-like fish" , "Egg producer" , "Fish producing caviar" .)