海鮮丼は寿司より多くの魚と米が入っていますって英語でなんて言うの？

To express that Kaisendon has more fish and rice than sushi, you can state that, "There is more fish and rice in Kaisendon than in sushi."

If something is supersized then it is a bigger version than normal. Sushi has rice, kaseidon has more. Sushi has fish, kaseidon has more. So kaseidon is a form of sushi - supersized!

"The dish kaisendon contains more fish than sushi does." Dish - a specific meal. Contains - what is inside. "The cup contains more water than the mug." You could also say "Kaisendon has more fish in it than sushi does." In it - in the dish. The quantity of fish is more in one dish than in the other.

This is to explain that Sushi does not have as much rice or seafood as another dish called Kaisendon.

Packed' means 'chocked full' or 'filled to the brim.' Use a semicolon (;) to separate sentence parts that need a more distinct break than a comma can signal, but that are too closely connected to be made into separate sentences. Typically these will be clauses of similar significance and grammatical form.

If something has something in it is it said to 'contain' it so wheat flour contains gluten more means that is has a larger amount than something else so you could say 'Kaisendon contains/has more fish and rice than sushi'

Contain means something inside/include in it. Example " How much water do you think this bottle contains?"