In Polish when you say "ryba" it generally refers to a single fish. It is however correct to say "dziś na obiad jest ryba" (today's dinner is fish) even if in fact we cooked more than one fish. But fish is countable in Polish, so in other cases we tend to use the plural form "ryby".
"kobiety" is Nominative and Accusative plural (and Vocative as well, but that is really rare), but also Genitive singular. Not Dative.
The exact same thing is true for "ryby" and almost any other feminine noun.
So @JaniceDubr whatever the sentence about a singular woman was, it must have taken Genitive case, not Accusative like this one.
Ok, so its all Greek to me. Where can I learn about "nominative, accusative, vocative, genitive and dative". I am completely lost with these terms and it seems they are so integral to learning Polish that I have to bite the bullet and try to understand. I think I am learning the way a young child does in that I go with what "sounds right", but that isn't enough!