One cookbook states that the dish typically consists of "a fifty-fifty mix of lean and oily fish" along with shellfish such as clams and mussels and often squid or octopus as well.[1] This recipe uses two kinds of oily fish (such as mackerel, swordfish, or tuna) and two kinds of lean whitefish, (such as cod, monkfish, hake, flounder and haddock), plus shrimp, mussels in the shell and squid.[3]