Which types of fish in sushi must be cooked?

All of the following are generally cooked items:

• Shrimp, ebi, available raw in sashimi, but almost always lightly poached. The poaching brings out sweet and subtle flavors otherwise masked by a metallic tang. It also prevents the highly perishable shrimp from losing texture to spoilage.

• Octopus, tako, available raw in sashimi when sliced very thinly, but otherwise poached lightly. The poaching reduces toughness and brings out additional flavors in an otherwise bland meat.

• Eel, unagi, as you noted, is ALWAYS grilled, and steamed. This is necessary to achieve the truly transcendent flavor and texture of unagi. In fact, the cooking of eel is such a challenge that it is generally a whole separate chef profession in Japan. Most eel comes from one of the professionals, because sushi cooks know they will never be able to match the quality themselves. Improperly cooked eel becomes tough and has unpleasant flavors. Raw, the blood of eels is even toxic!

• Sweet egg omelet, tamago, is by definition cooked. This is not to say that raw egg doesn't have a place in Japanese food though; tamago kake gohan is a dish of raw egg on rice, with soy sauce.

• Cockle is lightly poached

• Crab, kani is always cooked because... well eating raw crab meat is just vile.

For further reading, I highly suggest the online sushi encyclopedia.

Food Safety:

Sushi is only prepared from the very freshest and highest quality seafood, and sushi chefs are trained to identify parasites and signs of spoilage. In addition, some areas (including the EU) require sushi to be frozen for 24 hours to kill parasites.

If that wasn't enough to help settle your stomach, the pickled ginger and wasabi served along with sushi are more than garnish or simple condiments! Both ginger and wasabi have potent and documented anti-microbial and anti-parasite properties. Ginger is also well-known for combatting nausea. Source: the CRC Handbook of Medicinal Spices, page 310 for wasabi and 316 for ginger. (links are to Google Books copy).

There are a couple of other sushi ingredients that are usually cooked:

• Shrimp starts to break down very soon after being caught so is poached ASAP. After that it's not usually cooked, however.

• Octopus is poached when used for sushi, but kept raw for sashimi, where it is sliced very thinly. It is cooked for sushi to improve the flavour.

Sushi fish is generally of a better standard than other fish, and is subject to more rigorous controls. FDA regulations require all sushi fish to be frozen at -20 degrees for 24 hours in order to kill parasites. In addition, sushi chefs are trained to look for signs of spoiling or parasitic infection.

In addition to the already mentioned I have seen the following:

• Cooked Tuna in more western style sushi such as spicy tuna roll
• Shirako (cod sperm sack) is also used cooked in gunkan
• Seared fish some fish such as tuna and, in Japan especially salmon is often seared with a blow torch on the nigiri

Food Safety:

A common misconception is that the fish needs to be as fresh as possible which is not true in all cases. In high end sushi restaurants part of the skill is to age the fish appropriately to bring out more complex flavors similarly as is done with beef. In general, larger darker fish such as tuna would be considered most delicious 1 week to 10 days after the catch while smaller lighter coloured fish would only be aged for a day. To accomplish this without the fish spoiling the fish should ideally be killed using the ikejime method https://youtu.be/TS4AM9mPX-8