Final answer:
The friend should include sushi but avoid using raw shellfish due to the risk of parasitic infections like those from Diphyllobothrium species or fish tapeworms. Freezing or cooking shellfish is safer for consumption.
Step-by-step explanation:
Your friend plans to open a Japanese restaurant that will feature shellfish and will need to include sushi while avoiding raw shellfish due to health risks. A concern when consuming raw fish, like those found in sushi and sashimi, is the risk of parasitic infections such as those caused by Diphyllobothrium species or fish tapeworms. Undercooked salmon, frequently used in sushi, has been linked to an increased rate of these infections historically.
It is recommended that fish be frozen or cooked before eating to kill harmful worms and larvae. Therefore, while sushi with cooked or frozen fish is generally safe, your friend should avoid serving fresh, raw shellfish to prevent potential health risks.