Bad-tempered teetotaller covered in fish (5)
I believe the answer is:
ratty
'bad-tempered' is the definition.
(I've seen this before)
'teetotaller covered in fish' is the wordplay.
'teetotaller' becomes 'tt' (abbreviation).
'covered in' indicates putting letters inside.
'fish' becomes 'ray' (ray is a kind of fish).
'tt' put within 'ray' is 'RATTY'.
(Other definitions for ratty that I've seen before include "Short" , "In a bad temper" , "Characteristic of pest" , "Bad-tempered, irritable as a rodent" , "with pests" .)