Fish from south not available in W Yorks city (4,3)
I believe the answer is:
sand eel
'fish' is the definition.
(sand eel is a kind of fish)
'from south not available in w yorks city' is the wordplay.
'from south' shows that the letters should be reversed in order.
'not available' becomes 'na' (abbreviation for not available).
'in' means one lot of letters goes inside another.
'w yorks city' becomes 'Leeds' (city in West Yorkshire).
'na' put inside 'leeds' is 'leednas'.
'leednas' reversed gives 'SAND-EEL'.
(Other definitions for sand eel that I've seen before include "Very small fish that burrows into beaches" , "swimmer" , "Shallow-water fish" .)