Traveller rejected cold and hot fish (5)
I believe the answer is:
perch
'fish' is the definition.
(perch is a kind of fish)
'traveller rejected cold and hot' is the wordplay.
'traveller' becomes 'rep' (travel company worker).
'rejected' says the letters should be written in reverse.
'cold' becomes 'c' (eg on taps).
'and' is a charade indicator (letters next to each other).
'hot' becomes 'h'.
'rep' written backwards gives 'per'.
'per'+'c'+'h'='PERCH'
(Other definitions for perch that I've seen before include "Fish and old measure" , "(Fishy) pole where bird sits" , "What angler may catch" , "Roost; old measure" , "Freshwater fish - roost" .)