Fish from part of boat docked over vasty extremes (7)
I believe the answer is:
anchovy
'fish' is the definition.
(anchovy is a kind of fish)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for anchovy that I've seen before include "Small fish used in making sauce, paste etc" , "Small salty fish" , "Tiny fish, usually canned" , "Small fish of herring family, nice on toast" , "Salty little fish" .)