Wandering island for a bit of fish (6,3)
I believe the answer is:
dorsal fin
'a bit of fish' is the definition.
(I've seen this before)
'wandering island for' is the wordplay.
'wandering' is an anagram indicator.
'island'+'for'='islandfor'
'islandfor' anagrammed gives 'DORSAL FIN'.
(Other definitions for dorsal fin that I've seen before include "Projection on back of fish" , "swimmer? Just a bit" , "Stabilising appendage on a fish's back" , "All that may be seen of shark" , "bit of fish" .)