Bonito flakes are flakes of dried, smoked bonito fish. They look similar to wood shavings. The "bonito" is a type of tuna, but may not be marketed as tuna in many countries. Found in Asian Food Markets or online. Use for dipping with shabu-shabu, and use on fish and shellfish dishes as a marinade. This sauce is also used to baste fish as it cooks also. It’s uses are versitile, and you can also used as a marinade for beef. If you can't find Yuzu juice you can substitute lime juice, but you won’t get the distinctive flavor that yuzu imparts.