Leaning over and grabbing, first, the fish (7)
I believe the answer is:
listing
'leaning over' is the definition.
'listing' can be an answer for 'leaning' (thesaurus). I am not sure about the 'over' bit.
'grabbing first the fish' is the wordplay.
'grabbing' means one lot of letters goes inside another.
'first' becomes 'ist' (ist resembles 1st).
'the fish' becomes 'ling' (ling is a kind of fish).
'ist' inserted within 'ling' is 'LISTING'.
'and' is the link.
Can you help me to learn more?
(Other definitions for listing that I've seen before include "Enumerating" , "Keeling over" , "catalogue" , "Not going straight" .)