Niddah 23 - Animal
If a woman aborts something resembling a fish, a locust, or a rodent, this is not considered birth, and she is ritually pure, if there was no blood. If she aborts something resembling domesticated animal, wild animal, or fowl, then Rabbi Meir says that she observes the waiting periods as if she gave birth to a human , but the Sages say that only a human-like form considered birth for the purposes of ritual purity.
We can understand the Sages, but how does Rabbi Meir arrive at his point of view, and why does he not include the likeness of a fish? Some say, this is because the term "created" was used in conjunction with human and with animals. But "created" is also used in "And God created large sea creatures!?" - This is a difficulty that the Talmud explains by analyzing the use of the extra word, "created" in different context. Other say, this is because animal eyes resemble those of humans.
Rabbi Yirmiyah asked Rabbi Zeira, "According to Rabbi Meir, who considers the shape of an animal like a human in some way, what if this animal is a female, and its father accepted a marriage proposal money from a man for it - can that man marry her sister?"
Rav Adda bar Ahava asked Abaye, "What if - the other way around - an animal gives birth to someone resembling human, would Rabbi Meir say it is a human?" What difference does it make? - In the case where the mother animal was slaughtered before giving birth, would her ritual slaughter allow to eat this creature, like it does for normal animals?
Art: Clara Peeters - Still Life of Fish and Lemons