Servant’s opening can of silvery American fish (8)
I believe the answer is:
stingray
'fish' is the definition.
(stingray is a kind of fish)
'servant's opening can of silvery american' is the wordplay.
'opening' indicates taking the first letters.
'can of' becomes 'tin' (I can't justify this - if you can you should give a lot more credence to this answer).
'silvery american' becomes 'gray' (US spelling of 'grey').
The first letter of 'servants' is 's'.
's'+'tin'+'gray'='STINGRAY'
(Other definitions for stingray that I've seen before include "Marine creature with venomous tail" , "Poisonous spined fish" , "Large venomous fish -- it's angry (anag)" , "Fish with venomous tail" , "Dangerous fish" .)