If you take a look through the freezers at your friendly neighborhood bait shop, you’ll find an assortment of options. Of course there are shrimp, but there are probably also many other choices: Mullet, sardines, whitebait, clams, crabs and a bunch of other stuff. All of them catch fish, but there’s a time and place each is most effective.
One of the most common frozen baits is squid. Squid are one of the most important food sources for saltwater fish worldwide, so they’re an important bait. Sometimes you’ll find whole small squids; other times, large or small pieces of “wing” from larger squid. I generally prefer large wing pieces for offshore fishing and smaller chunks for inshore applications, but whole squid are useful for some purposes.