1d. Already decided when presented without the carp... (6) ?R?S??
(Is a WRASSE a type of carp?)
13a. About a gland in dirty halo (9) ??Y?O?D?L
(Only word that fits seems to be AMYLOIDAL but I can't see what starch or starchiness has to do with clue). And if 1d. is WRASSE then this will make the first of 13a letter E.
23d. Biting serve contraction (6) A?E?I?
(ACETIC fits, contraction could be referring to TIC, but I don't get the rest)