I've seen how people tell us to think of "du" as ""some" but I think that doesn't mean it's a direct translation. It's just so we can understand the reason they use "du" instead of not using an article at all. I think "du" is used because they never omit the article in french. So they say simply "The man is eating fish" and there's no need for article. In the case that english had obligatory articles then the closest one to understand is "some". So it can be translated like that and it's a valid option. But, again, it's not a direct translation. So when I see "du" in a translation exercise I just omit the article in english and the "some" would be optional, just in case it feels appropriate.