Interesting that "We are eating a different fish" was the suggested "correct" answer.
I do think that we can say "We are eating a different fish" when we mean that we are eating a different kind of fish.
That would mean that some "we" (let's say George and Sue) are eating the same fish, but it's a different fish than someone else (Peter) is eating. There's plural in the Polish sentence.
Why can't you say. We are eating a different fish? As different should also be an option as for other.
We are eating other fish is awkward English. A regular speaker would likely never say that, maybe someone transliterating into English. The Polish equivalent may be acceptable in the language but definitely not for someone learning English.
The fish are different from each other, or both of then are different from the rest of the fish in the world?
It should be "We are eating other fish [here "fish" is plural so "other" not "another"]"
No reason. The guy who set up the exercise may know Polish, but his English is very poor.
Ryb and ryby both are plural. Is ryby also ever used to describe a single fish? What about rybny? Is it plural as well?..
We could start from examining declension pattern of the word ryba.
Case: singular vs plural
Nominative: ryba vs ryby
Genitive: ryby vs ryb
Dative: rybie vs rybom
Accusative: rybę vs ryby
Locative: rybie vs rybach
Instrumental: rybą vs rybami
Vocative: rybo vs ryby
As you can see there is 7 cases, both singular and plural. But there is only 10 versions of the word. Ryby occurs 4 times!
Rybny is an adjective derived from ryba and means one that have fish. Could be river, pond or shop.
This is terrible English. I suggested "We are eating a different fish" and was marked down.
That's because the Polish fish word is plural, so "a" cannot apply here.
my answer we are eating different fish was accepted; so can this mean I have a selection of fish of which I am eating or only mean I am eating different fish from say that which I was eating previously? ie i am eating other fish
We are now eating tuna and halibut although previously we were eating salmon and catfish.
You and me are eating different fish (you're eating tuna, I'm eating halibut, or you're eating tuna and halibut, I'm eating salmon and catfish, etc.).
Both should have worked. However, I see a report that is most likely yours (from 2 hours ago as of the moment I'm writing this), and it says "We are eating a different fish". With a singular fish, while there's plural in the original sentence.