Oktzim, Chapter Three, Mishnah Eight
1) When do fish become susceptible to uncleanness?
a) Bet Shammai say: after they have been caught.
b) Bet Hillel say: only after they are dead.
c) Rabbi Akiva says: if they can still live.
2) If a branch of a fig tree was broken off, but it was still attached by its bark:
a) Rabbi Judah says: [the fruit] is still not susceptible to uncleanness.
b) But the sages say: [it all depends] whether they could still live.
3) Grain that had been uprooted, but is still attached to the soil even by the smallest of roots, is not susceptible to uncleanness.
Section one: Fish can be eaten without first being slaughtered. Indeed, theoretically one could catch a fish from the sea and immediately eat it even while it’s still alive (there definitely are cultures that do this). Therefore, Bet Shammai says that fish are immediately susceptible to impurity, once they have been caught, for they are immediately considered food.
Bet Hillel says they are not food until they are dead, because that’s when they are generally eaten.
Rabbi Akiva takes a position somewhere between the two houses. If the fish is still currently alive but will die even if it were thrown back into the water, then it is already considered food and is susceptible to impurity. But if the fish has been caught but could still be thrown back into the water and live, then it is not susceptible.
Section two: A similar case is brought with regard to branches that have been cut off a tree but are still hanging by their bark. Fruit on a tree is not susceptible to impurity but once it has been cut off it is. Rabbi Judah says that as long as the fruit is hanging by its bark, meaning it is still attached, it is not susceptible. The other sages say that it all depends on whether the fruit is attached enough such that it could live. Like the fish, if the fruit could still live, it is not susceptible to impurity.
Section three: Grain is not susceptible to impurity until it has completely been severed from the soil