Carp, sigh and fold up (8)
I believe the answer is:
goldfish
'carp' is the definition.
(I've seen this before)
'sigh and fold up' is the wordplay.
'and' means one lot of letters go next to another.
'up' is an anagram indicator (letters get chucked up).
'sigh' put after 'fold' is 'foldsigh'.
'foldsigh' with letters rearranged gives 'GOLDFISH'.
(Other definitions for goldfish that I've seen before include "one enjoying pond life?" , "Popular piscine pet" , "Swimmer in a bowl" , "Ornamental reddish Chinese carp (8)" , "Small orange carp" .)