Like the doubtful activities of a shark (5)
I believe the answer is:
fishy
'the doubtful activities of a shark' is the definition.
I can't judge whether this defines the answer.
'like' is the wordplay.
I cannot quite understand how this works, but
'like' could be 'ish' (similar in meaning) and 'ish' is found in the answer.
The remaining letters 'fy' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for fishy that I've seen before include "Dodgy, suspicious" , "Arousing suspicion" , "Dubious - piscatorial" , "Suspect" , "Suspicious, shady" .)