Suspicious (5)
'suspicious' is the definition.
(I know that suspicious can be written as fishy)
This is all the clue.
(Other definitions for fishy that I've seen before include "As smelt, perhaps" , "Suspicious (as trout?)" , "Dodgy, suspicious" , "Dubious - piscatorial" , "Suspicious, shady" .)
(Other definitions for leery that I've seen before include "Shy" , "Cunning - wary" , "Sly, cunning" , "Cautious due to suspicions" , "Suspiciously cautious" .)