"One fish, two fish, red fish, blue fish"
Translation:Én fisk, to fisk, rød fisk, blå fisk
Either works. Please see my response to CanLiang below.
When does the e in "en" need an accent as shown here. Pretty sure this is the first time I've encountered that.
When "én" replaces the number "one", it often gets the accent added, especially if there's a reason to stress the number. The accent is still optional.
When "en" functions as an indefinite article, it's never accented.
It's a rhyme, and the name of a Dr. Seuss book (see the image up top).
The adjectives are in their correct form, indefinite m/f, to match up with the noun "fisk". The neuter forms of the adjectives would be "rødt" and "blått" respectively.
"Fisk" works much like "fish" in English, in that the singular form is often used in a plural sense. "Fisker" would only be a strongly preferred plural in cases where each individual fish was in focus. When using it strictly as a mass noun, "fisk" would be preferred, and in all other contexts you have two options.
For example, if someone were to ask you how much fish you caught on your trip, both "Jeg fikk fem fisk" and "Jeg fikk fem fisker" would be correct.