Thou shalt not sleep with the fishes

Summary: Considering a derasha from Rav Chaim Kanievsky. Plus my own tongue-in-cheek interpretation of the pasuk.

Post: In Taama deKra, Rav Chaim Kanievsky takes careful note of the language within one pasuk:

21. Cursed be he who lies with any animal. And all the people shall say, 'Amen!'

כא. אָרוּר שֹׁכֵב עִם כָּל בְּהֵמָה וְאָמַר כָּל הָעָם אָמֵן:

"אָרוּר שֹׁכֵב עִם כָּל בְּהֵמָה -- this requires consideration, why is the word כל necessary, and it would not have been sufficient to write עִם בְּהֵמָה. And there is to say that it comes to include the dolphinin {=mermaids}, which are half human and half fish, who bear and raise from {J: rather than 'like' humans}. (See Bechorot 8a, and Rashi and Tosafot.) That even so, one who has intercourse with them is liable for bestiality, for its law is like that of an animal and not like a human."

While this particular derasha was never said by Chazal, but rather seems to be introduced by an Acharon, namely R' Kanievsky, it follows the pattern of other derashot, of כל to include, and to include something you might not have expected, for some reason.

Alas, she is Biblically forbidden.

The gemara in Bechorot 8a reads (starting on the previous amud):

ת"ר דג טמא משריץ דג טהור מטיל ביצים כל המוליד מניק וכל המטיל ביצים מלקט חוץ מעטלף שאף על פי שמטיל ביצים מניק הדולפנין פרין ורבין כבני אדם מאי דולפנין אמר רב יהודה בני ימא

(I actually discuss the first part of this brayta, about the atalef / bat, at great length in this other post.) The end of the brayta, and the comment by Rav Yehuda, read:

Dolphins are fruitful and multiply by coupling with human beings. What are dolphins? — Said Rab Judah: Humans of the sea {=bnei yama}.

The gemara is slightly unclear and ambiguous, so we can turn to Rashi, who says:

ה"ג הדולפנין פרים ורבים מבני אדם - שאם בא אדם עליהם מתעברות הימנו:

בני ימא - דגים יש בים שחציין צורת אדם וחציין צורת דג ובלע"ז שריינ"א:

Rashi changes the girsa from פרין ורבין כבני אדם, like humans, into מבני אדם, with human beings. I would not have been so swift to change the girsa. Given the beginning of the brayta, which speaks of the methods of procreating for different species, and how birds in general lay eggs and nurse, it might have made a good deal of sense to point out that dolphins (rather than mermaids) give birth to live young, as opposed to fish which in general lay eggs. But instead, with the emended girsa, they procreate with humans. This may be a human / fish hybrid. Indeed, in the next comment, on bnei yama, he writes that they are 'fish which are half in human form and half in fish form, and in laaz they are called sirens {another name for mermaids}.'

Tosafot reinforces this emendation from Rashi by appealing to the Tosefta on Bechorot, which also has מבני:

הדולפנין פרין ורבין מבני אדם. כן גירסת הקונטרס וכן מוכח בתוספתא [פ"א] יולדין ומגדלין מבני אדם:

However, in our Tosefta, it does not say this at all. Rather:

הדולפינין מולידין ומגדלין כאדם.  דג טמא משריץ דג טהור מטיל ביצים.  קרבי דגים ועובר אין נאכלין אלא מן המומחה העוף נאכל במסורת נאמן צייד לומר עוף זה טהור.

(It is interesting that this particular gemara (Bechorot 8a) came up to resolve it. On the same page is cited another pasuk with ארור and בהמה, and כל, but it is a curse to the snake to be more cursed than all animals. It is one I might have paid attention to after a Bar Ilan or Snunit search for these search terms.)

Regardless of whether Rashi and Tosafot are right about the gemara, mermaids do not exist. So I would not be too hasty innovating a derasha on the basis of the Torah excluding them. Besides, is a dag really considered a beheimah?

The more obvious derasha, though one that does not really work out, is as follows:
אָרוּר שֹׁכֵב עִם כָּל בְּהֵמָה -- only if he slept with every animal. But if he only slept with a few animals, or a few species, he would not be אָרוּר.

Of course, the only one who did that was Adam haRishon. From the second perek of Bereishit:

23. And man said, "This time, it is bone of my bones and flesh of my flesh. This one shall be called ishah (woman) because this one was taken from ish (man)."		כג. וַיֹּאמֶר הָאָדָם זֹאת הַפַּעַם עֶצֶם מֵעֲצָמַי וּבָשָׂר מִבְּשָׂרִי לְזֹאת יִקָּרֵא אִשָּׁה כִּי מֵאִישׁ לֻקֳחָה זֹּאת:
This time: This teaches us that Adam came to all the animals and the beasts [in search of a mate], but he was not satisfied until he found Eve. — [from Yev. 63a]		זאת הפעם: מלמד שבא אדם על כל בהמה וחיה ולא נתקררה דעתו בהם עד שבא על חוה:

Though this was before mattan Torah, and with Hashem's OK, so he would not have been cursed for it.