"We eat good fish with vegetables."
Translation:Wir essen guten Fisch mit Gemüse.
Accusative case, masculine noun, no preceding article = strong inflection. See chart here: http://en.wikipedia.org/wiki/German_declension#Strong_inflection.5B6.5D.5B7.5D
I'm not a native speaker, but I believe the German language doesn't use Fisch as a mass noun, so you have plural and singular versions of the word. If you wanted to translate the English as plural, and keep the German as plural, you would have to write "Wir essen gute Fische mit Gemüse". "Gute" - accusative, plural, strong inflection. "Fische" - plural of Fisch. If given the English sentence and asked to translate to German, I believe both answers should be accepted. Whether they are or not, I don't know.