Fishy sort of deer? (3)
I believe the answer is:
roe
I believe this is a double definition.
'fishy sort' is the first definition.
(thesaurus)
'deer?' is the second definition.
(roe deer is a kind of deer)
'of' acts as a link.
(Other definitions for roe that I've seen before include "If hard, eggs" , "Fish eggs; small deer" , "Hoofed animal(s)" , "Part of fish, sounds like go through water" , "eg Caviare" .)