For the last few pages, the Talmud has been examining odd cases of animals that spawn offspring of an (apparently) different species. There is a question of whether such an offspring can attain firstborn status, which the Gemara ruled is dependent on whether the animal still has some characteristics of the mother animal. But there are other questions as well — such as kashrut. The mishnah states:
In the case of a kosher animal that gave birth to a non-kosher animal of sorts, its consumption is permitted. And in the case of a non-kosher animal that gave birth to a kosher animal of sorts, its consumption is prohibited. This is because that which emerges from the non-kosher animal is non-kosher and that which emerges from the kosher animal is kosher.
The offspring is considered kosher if, and only if, its mother is kosher — regardless of whether it appears to be a kosher species itself. This, in turn, leads to a question of one fish found in the belly of another fish which, presumably, swallowed it. The mishnah on today’s daf states:
In the case of a non-kosher fish that swallowed a kosher fish, consumption of the kosher fish is permitted. And in the case of a kosher fish that swallowed a non-kosher fish, consumption of the non-kosher fish is prohibited due to the fact that the host fish is not the place of its development.
In this case, the kashrut status of the fish that has been swallowed is unaffected by the status of the fish that consumed it. Being swallowed is fundamentally different from being gestated.The Gemara now makes an inference from the mishnah’s language:
The reason consumption of the kosher fish is permitted is that we saw that the non-kosher fish swallowed the kosher fish. But if we did not see it swallow the kosher fish we say that perhaps the non-kosher fish spawned the kosher fish.From where do we derive that we must have this concern? As it is taught in a beraita: A non-kosher fish spawns offspring, while a kosher fish lays eggs.
The mishnah was precise when it said “a non-kosher fish that swallowed a kosher fish,” and not “a kosher fish found inside a non-kosher fish.” Specifically, when we witnessed the swallowing, we can be confident that the kosher fish in the non-kosher fish’s innards is the same one we just saw. But if I cut open a non-kosher fish and find what looks like a kosher fish inside of it, I should worry lest that fish is in fact the offspring of the non-kosher fish, which the rabbis claim spawns offspring inside its body, as opposed to a kosher fish which lays eggs.
Now the Gemara has a new problem: If non-kosher fish are known to spawn offspring inside their bodies, how do we know that a fish found inside the non-kosher fish was swallowed? If I see a catfish (not kosher) swallow a tuna (kosher), and upon cutting open the catfish I find a tuna inside, perhaps I should be worried that the actual kosher tuna has been digested, and the intact tuna I’ve found is actually a hybrid the catfish spawned, and therefore treif!
The rabbis offer several resolutions to this dilemma:
Rav Sheshet says: It is referring to a case where one found the kosher fish in the digestive tract.
Rav Pappa says: It is referring to a case where one found the kosher fish in the passageway of the gullet.
Rav Nahman says: It is referring to a case where one found it whole.
These amoraim all note that the location or physical state of the kosher fish might be a sure enough indicator that it was swallowed rather than spawned. In so doing, they’re all seemingly conceding the Gemara’s first point: If we didn’t witness the catfish swallowing the tuna, the latter is always suspected of being spawned by the former. But Rav Ashi suggests otherwise:
Rav Ashi says: The majority of fish spawn offspring of their own species, and therefore the case of a kosher fish discovered inside a non-kosher fish is considered as if the non-kosher fish had swallowed the kosher fish in our presence.
Rav Ashi says the likelihood of a catfish spawning an offspring that looks like a tuna is small enough that should I find tuna inside a catfish, I can confidently state the tuna was swallowed (and not spawned) by the catfish, even if I didn’t witness it with my own eyes. Food for thought, as it were.
Read all of Bekhorot 7 on Sefaria.
This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on September 24, 2026. If you are interested in receiving the newsletter, sign up here.
Curious Minds Welcome. Whatever you're wondering about Judaism, My Jewish Learning has an answer, and it's free because readers like you make it so. Give to open more doors for Jewish discovery.
