"The fish is not fresh any more."
Translation:Der Fisch ist nicht mehr frisch.
"Noch" translates as yet or stll, whereas the words, "nicht mehr" mean no more (or not more). So, if you use ""noch" you might be missing out on the negative, depending on the overall wording.
(It's best to quote your full answer.)
(If you think you might want to, select and copy before you click on "Check"!)