how can you use fresh fish to make sushi???? The safe sushi-grade fish should be frozen at 0°F for 7 days or flash-frozen at -35°F for 15 hours to kill parasites. See www.kobejones.com.au/how-to-choose-sushi-grade-seafood/#:~:text='Sushi%2Dgrade'%20fish%20is,%C2%B0F%20for%2015%20hours.