Negitoro is the seafood version of steak tartare.
For negitoro made from red-fleshed fish, commonly used substitutes for tuna include opah (often referred to as "moonfish" or "sea salmon"), bigeye tuna, and yellowfin tuna. Despite its name, opah is not related to the sunfish family, but rather belongs to the same group as the oarfish. Opah has a flavor and texture similar to tuna, and its red-fleshed parts are used in negitoro.
For fat content, fish such as amberjack or shark are often used. Shark fat, in particular, is frequently used as it closely resembles tuna fat, helping to recreate the taste of negitoro.
By combining these substitute fish and fats, the flavor and texture of negitoro can be replicated.
On the other hand, using escolar (oilfish) for fat could impart a rich, buttery flavor due to its high oil content. However, escolar contains indigestible wax esters, which, if consumed in large quantities, can cause digestive issues such as "keriorrhea," leading to oily, orange-colored stools. While escolar fat might enhance the richness of negitoro, its potential for causing digestive problems means it is often avoided in many regions.