Rice of course is halal as far as I know, but what about of other seafood that can be used when cooking sushi such as shrimps, crabs, salmon, caviar etc?
There are some ingreidents in Sushi that need investigation.
Welcome to our site. You're asking a question that's both easy and difficult.
First, from the basics: all food is halal until proven haram. If there's something which you're not sure about, by default, you should consider it okay to eat. Most of the porhibitions are well-established in scripture (Qur'an and hadith), including:
On the other hand, anything from the sea is okay to eat (5:96).
These are the basic rulings that come into play with sushi. Whether food is permissible or not depends on these general maxims, as well as other, specific maxims, such as not eating predators, avoiding flambee, ingredients derived from animal sources that are not in super small quantities, etc.
I suggest some research, and finding out what's in the sushi -- looking at the ingredient list.