The first fish on platters (5)
I believe the answer is:
trays
'platters' is the definition.
(I've seen this in another clue)
'the first fish on' is the wordplay.
'first' indicates taking the first letters.
'fish' becomes 'rays' (I've seen this before).
'on' says to put letters next to each other.
The first letter of 'the' is 't'.
't'+'rays'='TRAYS'
(Other definitions for trays that I've seen before include "Shallow carriers" , "Salvers" .)