When I read recipes involving boiling a soup/dessert and adding sugar, they often say to add the sugar towards the end of the boiling.  Why is that?  Are there consequences of adding sugar early? 
Live parasitic worms are to be expected in raw fresh fish, and need to be dealt with in one of three ways:   Cooking: If the fish is thoroughly cooked, the worms will be dead and safe to eat. Removal/avoidance: A skilled sashimi chef has an eye for parasites, and will either discard contaminated pieces, or remove the parasites. Freezing: So called "sushi grade" fish is fish that has been frozen at a temperature/duration recommended by the US FDA. That's 7 days at -20°C, or colder for shorter treatments. Note that this is much colder than domestic freezers. It is said to provide a "parasite destruction guarantee".   There may be other ways to neutralise parasites, such as Eskimo-style fermented fish - but these are unlikely to be of use to you.  There is a difference between safety and palatability, though, and your customers might reasonably expect to be served fish without visible parasites. 