פירוש על עבודה זרה 79:9

The kalbit fish is a sign that the brine is kosher. So if the barrels are open, one kalbit fish is sufficient for all of the barrels to be presumed kosher. But if the barrel is closed, then only that barrel can be considered kosher. The others must be suspected as coming from non-kosher fish. Interestingly, R. Hinena calls Rav, Shmuel and R. Yohanan “verses” as if to say that they are as reliable as the written word.