"De vissen drinken water."
Translation:The fish drink water.
Fish is both singular and plural. A fish = een vis, fish = vissen. Somebody else pointed out somewhere that fishes is used in a biblical phrase, but outside of that it's almost never used to refer to fish. Fishes can be used as a verb, i.e. He fishes for an answer.
Fishes is used to describe different kinds of fish (f.e. if you talk about haddocks, herrings and codfish, these could be summed up as fishes). Would vissen apply to this definition as well?
Interesting information, thanks! As a French speaker, I have to use the English interface to learn Dutch, and I had no idea about this subtlety with the word "fish". The word "fishes" is stated as the plural form in dictionaries without any given context though. Shouldn't this section of this lesson be corrected to accept both forms, then?