which is up (by) numbers

"That means the country sold close to 2.3 billion dollars worth of goods overseas everyday, up four-and-a-half percent on-year."

I have seen the passage and I was wonderinf if "by" is omitted or optional in ,up four- and - a- half percent on - year like ,(by) up...
because up + numbers is weird to me. What do you native English speakers think?

Thank you so much ad usual.