You can buy sushi-grade fish from a trusted grocery store, fishmonger, or local Asian market. Ask if the fish has been previously frozen (ideally to at least -31°F, or all the way down to -20°F) to kill off any parasites and prevent any pathogens from growing. As a general rule, it’s worth noting that fish farmed in the USA, Norway, Britain, New Zealand, Canada, or Japan should be safe to eat. These countries have strict standards in regards to cleanliness and are typically free from parasites.