Fish, after swallowing maiden, left people alone mostly (3,6)
I believe the answer is:
red salmon
'fish' is the definition.
(I know that red salmon is a type of fish)
'swallowing maiden left people alone mostly' is the wordplay.
'swallowing' indicates putting letters inside.
'maiden' becomes 'm' (cricket abbreviation).
'left people' becomes 'reds' (red is a kind of person. I am not sure about the 'left' bit.).
'mostly' means to remove the last letter.
'alone' with its last letter taken away is 'alon'.
'reds'+'alon'='redsalon'
'm' put inside 'redsalon' is 'RED SALMON'.
'after' acts as a link.
Can you help me to learn more?
(Other definitions for red salmon that I've seen before include "Sockeye" , "fish" .)