There is. Usually the first sea day. They even keep passengers with jeans out of one main dining room. You will not find many in formal dress but most dress up a bit. Some suits, some jackets and ties, most in nice shirt and slacks.
Thanks! This is my first cruise and this forum has been great with people like you who have been there. It helps to pour through the previously asked questions and if my questions aren't answered there, I post a new one.