If I'm understanding you correctly, you could do something like this:

use strict;
use warnings;
my @FieldNames =
   (
     'One'
   , 'Two'
   , 'Three'
   , 'Four'
   , 'Five'
   )
;

print join ':', shift(@FieldNames), join ',', @FieldNames;
[download]

or if you want a non-destructive technique, you could use array Slices:

print join ':', $FieldNames[0], join ',', @FieldNames[1..$#FieldNames];