"The dolphin eats fish."
Translation:Le dauphin mange des poissons.
Fish is both singular and plural in English.
If the English sentence was referring to a single fish, it would say, "The dolphin eats a fish." By skipping the article ('a'), the plural noun is implied.
When an adjective is placed before a plural noun, des becomes de.
Le dauphin mange des poissons. ~ No adjective.
Le dauphin mange de petits poissons. ~ Adjective before noun.
Le dauphin mange des poissons roses. ~ Adjective after noun.
Because le dauphin is the noun for the dolphin regardless of the mammal's gender. There is no feminine noun. La dauphine actually means something else.
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