Fish for fresh char, catching nothing (5)
I believe the answer is:
roach
'fish' is the definition.
(roach is a kind of fish)
'fresh char catching nothing' is the wordplay.
'fresh' indicates an anagram.
'catching' means one lot of letters goes inside another.
'nothing' becomes 'o' (looks like zero - 0).
'char' anagrammed gives 'rach'.
'rach' enclosing 'o' is 'ROACH'.
'for' is the link.
(Other definitions for roach that I've seen before include "member of family carp" , "Silvery freshwater fish" , "Swimmer" , "Freshwatwer fish" , "Fish - part of a cannabis cigarette" .)