Before us is Mishnah 8 in chapter 10, which continues the discussion of pickling and the transfer of taste. Here Terumah is not the subject at all; rather, the issue is the transfer of taste between non-kosher fish and kosher fish that are pickled together in a single barrel. What is distinctive about fish is their strong, sharp taste, and for that reason the required ratio of permitted substance against forbidden substance in a mixture rises.
The View of the Tanna Kamma:
The Mishnah discusses a barrel in which non-kosher species of fish were pickled together with kosher species of fish, the entire contents amounting to two se'ah. A se'ah is conveniently estimated as about six two-liter bottles, that is, about twelve liters, so two se'ah come to about twenty-four liters, roughly six or seven gallons.
If within those two se'ah there is even a small quantity of non-kosher fish, "k'mishkal asarah zuz biYehudah, shehem chamesh sela'im baGalil" - that is, the weight of ten zuz coins in Judea, which equal five sela coins in the Galilee - everything is forbidden. This ratio comes out to one part in nine hundred and sixty, and all the liquid in the vessel becomes forbidden, because non-kosher fish imparts an extremely strong taste.
The halachah follows this view, except that the measure is rounded off to a thousand. Practically speaking, if we set aside the view of the Rambam - and certainly according to the Ashkenazim, and in practice according to everyone - one needs a thousand times as much permitted substance against the forbidden component of non-kosher fish mixed into the mixture.
The View of Rabbi Yehudah:
Rabbi Yehudah disagrees and says: "revi'is b'sasayim" - the threshold is a single revi'is, the size of a kiddush cup, which is a quarter of a log, within two se'ah.
The System of Measures: These terms are useful and familiar, and they are worth knowing:
Se'ah - about six two-liter bottles, and it divides into six kabin.
Kav - about one two-liter bottle, and it divides into four lugin.
Log - about five hundred cc, about the size of a small cola bottle.
Revi'is - a quarter of a log, about one hundred and twenty-five cc. This measure lands almost exactly midway between the view of Rav Moshe, and even the view of Rav Chaim Naeh, and the view of the Chazon Ish.
Working backwards, we get the following: in one se'ah there are six kabin, which are twenty-four lugin, which are ninety-six revi'iyos. And in two se'ah there are one hundred and ninety-two revi'iyos. It emerges, then, that the view of Rabbi Yehudah requires one hundred and ninety-two times as much permitted substance against the forbidden substance in fish brine for the mixture to be permitted; and if the ratio is exactly one in one hundred and ninety-two, it is still forbidden.
The Rema rules like Rabbi Yehudah, except that he rounds the measure off to two hundred: two hundred parts against one - permitted, and less than that - forbidden.
The View of Rabbi Yosei:
The third measure is that of Rabbi Yosi, who says: "Echad b'shishah asar" - the threshold is one part in sixteen, and there must be more than one part in sixteen. The source of this measure is unclear, and we have not found anyone who explains where this number was derived from.
In summary: there are three opinions in the Mishnah regarding the amount needed to nullify the taste of a non-kosher fish in a mixture: the Tanna Kamma - one part in nine hundred and sixty; Rabbi Yehudah - a revi'is in two se'ah, which is one part in one hundred and ninety-two, and the Rema rounds it up to two hundred; and Rabbi Yosi - one part in sixteen. The halachah follows the Tanna Kamma, and this is because the taste of sea water and fish brine is extremely strong, and therefore a thousand times as much permitted substance is required against the forbidden one in order for the mixture to be permitted.