Fish thrash around wildly (8)
I believe the answer is:
flounder
I believe this clue is a double definition.
'fish' is the first definition.
(flounder is a kind of fish)
'thrash around wildly' is the second definition.
(I've seen this before)
(Other definitions for flounder that I've seen before include "Flatfish - behave awkwardly" , "fumble?" , "Fish -- stumble helplessly" , "Catch" , "small swimmer" .)