Fungus found on a fish I see (6)
I believe the answer is:
agaric
'fungus' is the definition.
(agaric is a kind of fungus)
'on a fish i see' is the wordplay.
'on' is a charade indicator (letters next to each other).
'fish' becomes 'gar' (gar is a kind of fish).
'see' becomes 'C' (the word for the letter, according to Chambers).
'a' next to 'gar' is 'agar'.
'agar'+'i'+'c'='AGARIC'
'found' is the link.
(Other definitions for agaric that I've seen before include "Fungus, eg, mushroom" , "Fungus of mushroom family" , "Type of mushroom" , "fungal growth" .)