Fish needing both hands in sea (6)
I believe the answer is:
marlin
'fish' is the definition.
(I've seen this before)
'both hands in sea' is the wordplay.
'both hands' becomes 'rl'.
'in' means one lot of letters goes inside another.
'sea' becomes 'main' ('main' can be a synonym of 'sea').
'rl' inserted inside 'main' is 'MARLIN'.
'needing' is the link.
(Other definitions for marlin that I've seen before include "Prized game fish" , "Spearfish" , "Sea roamer" , "type of fish" , "Large sea-fish" .)