This is a "special Japanese dish" and shirako is another fancy name for an animal's reproductive organ. Shirako is essentially a cod's sperm sac. Apparently soft and creamy to taste you can have it served up steamed or deep fried. It is usually harvested from cod but can also be found from anglerfish, salmon, squid, and pufferfish. Shirako is mainly available in winter as this is when most types of the seminal fluid are in season
Although milt is a very common dish in Japan, many people consider it a rather acquired taste. It could be described as sweet and custardy; very subtle and delicate with a slight fishiness that makes it easily distinguishable from similar-looking dairy products. The texture of the sperm sac highly depends on the way it is served. While the raw Shirako is soft, creamy and slippery, it becomes slightly more firm and the individual sections become more defined when it is cooked.