Funazushi: Shiga's Ancient Fermented Sushi From Lake Biwa

Funazushi is made by salting nigorobuna, a crucian carp found only in Lake Biwa, then packing it in rice and letting it ferment for months to over a year. This nare-zushi method — fish preserved in fermented rice — is considered a direct ancestor of modern sushi, which split off once people started eating the rice too instead of discarding it. What you get today is closer to a strong, funky, cheese-like fermented fish than anything resembling a sushi roll.

The smell and sourness are polarizing even among Japanese diners, and it's genuinely an acquired taste rather than a crowd-pleaser — approach it as a piece of food history rather than expecting something mild. It's traditionally sliced thin and served as an accompaniment to sake rather than eaten in quantity. Nigorobuna populations have declined over the decades due to changes in the lake environment, so genuine Lake Biwa funazushi can be pricier and less widely available than it once was; check current sourcing if authenticity matters to you.