Some are made with primarilly fish, some with mostly shrimp. If you have even a slight reaction to shellfish, steer clear!
The sodium content is savage, that is the preserving agent. The old was was to pile layer after layer of either titi shrimp and 'chovies or just chovies with layers of salt and literally just wait for the fish to liquify.
Asia has its type, the romans had theres, Garum, used it on everything. Some of it was watered down with unfermented grape juice for wine (must) and used even more liberally.