Possibly a lost chance with no small fish (10)
I believe the answer is:
coelacanth
'fish' is the definition.
(coelacanth is a kind of fish)
'possibly a lost chance with no small' is the wordplay.
'possibly' indicates anagramming the letters.
'with no' suggests deleting specific letters.
'small' becomes 's' (abbreviation - e.g. clothes size).
'lost'+'chance'='lostchance'
'lostchance' with 's' taken out is 'lotchance'.
'a'+'lotchance'='alotchance'
'alotchance' with letters rearranged gives 'COELACANTH'.
(Another definition for coelacanth that I've seen is " bony fish".)