Fish a healthy red colour, tailless (4)
I believe the answer is:
rudd
'fish' is the definition.
(rudd is a kind of fish)
'a healthy red colour tailless' is the wordplay.
'a healthy red colour' becomes 'ruddy' (having a healthily red complexion).
'tailless' means to remove the last letter (the tail of the word is removed).
'ruddy' with its last letter taken away is 'RUDD'.
(Other definitions for rudd that I've seen before include "European freshwater fish" , "Red-eye fish" , "Freshwater fish of the carp family" , "Swimmer" , "Freshwater fish (silvery with red fins)" .)