In the episode "TKO" of the science-fiction show Babylon 5, Lt. Commander Susan Ivanova, a Jew, has dinner with her rabbi and they have a discussion about the food that they are eating.

Rabbi Koslov: What did you say this was again?

Ivanova: It's Treel. It's a sort of fish. The Centauri raise them.

Rabbi Koslov: Treel? It's kosher?

Ivanova: That, I can't say.

Rabbi Koslov: I don't recall Treel being mentioned in the Torah, so… [Takes a bite] It's wonderful.

The creator of the show, J. Michael Straczynski, stated that one version of the script delved further into whether or not Treel would be kosher, but found that it just didn't make for very good television:

At one point, there was a discussion in the scene about the whole gills/scales/fins issue, to define kosher...but it really brought the scene to a screaming standstill, and we needed to concentrate on the relationships at that moment. In addition, as we looked at it, you would have to get into the question of how alien gills/scales/fins compare to earthly gills/scales/fins, because they're going to be very different in many ways. In short order it became a massive Talmudic discussion, and we only have an hour for the show....

While we don't ever see a live Treel on the show and the shortened dialogue leaves few clues as to their nature, it seems clear from his statement that he thought there were significant enough differences that might lead to debate. Unfortunately, Straczynski didn't state what the outcome of that discussion might have been.

So would an alien fish be kosher? What might be the outcome of this discussion if there were time to consider the sort of differences in gills/scales/fins between an alien and earthly fish?

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    What basis would we have to research halacha about a fish that is imaginary?
    – DanF
    Commented Feb 17, 2015 at 22:24
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    Welcome to Mi Yodeya, and thanks for your fun question! Commented Feb 17, 2015 at 22:26
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    @AvrohomYitzchok consider judaism.stackexchange.com/q/50293/4794 Commented Feb 17, 2015 at 22:27
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    I have no source for this, but I would suspect that the answer would depend upon whether or not the fish's habitat can be halakhically considered a "sea" or a "river", or whether those terms denote bodies of water on earth. If its habitat is neither a sea nor a river, then the answer may be "yes", irrespective of whether or not it has scales and fins (cf: Rambam, Maakhalot Assurot 2:17).
    – Shimon bM
    Commented Feb 17, 2015 at 22:52
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    @AvrohomYitzchok This site has precedent for other questions about whether non-existent animals would be kosher (including dinosaurs and mermaids). Additionally, this might be something we might one day need to consider if, like in Babylon 5, future Jews are able to travel to other planets where they can get fish-like creatures different from those found on Earth. Commented Feb 17, 2015 at 23:03

1 Answer 1


It says in Sanhedrin 59b

כי הא דרבי שמעון בן חלפתא הוה קאזיל באורחא, פגעו בו הנך אריותא דהוו קא נהמי לאפיה, אמר: (תהלים ק"ד) הכפירים שאגים לטרף. נחיתו ליה תרתי אטמתא, חדא אכלוה וחדא שבקוה. איתיה ואתא לבי מדרשא, בעי עלה: דבר טמא הוא זה או דבר טהור? - אמרו ליה: אין דבר טמא יורד מן השמים. בעי מיניה רבי זירא מרבי אבהו: ירדה לו דמות חמור מהו? - אמר ליה יארוד נאלא! הא אמרי ליה: אין דבר טמא יורד מן השמים

As in the story of R. Simeon b. Halafta, who was walking on the road, when lions met him and roared at him. Thereupon he quoted: The young lions roar after their prey; and two lumps of flesh descended [from heaven]. They ate one and left the other. This he brought to the schoolhouse and propounded: Is this kosher or not? — They [the scholars] answered: Nothing non-kosher descends from heaven. R. Zera asked R. Abbahu: What if something in the shape of an ass were to descend? — He replied: Thou howling yorod: did they not answer him that no non-kosher thing descends from heaven? (Soncino translation)

It would seem from here that space fish would be kosher.

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    Are you assuming space and Heaven are the same thing? Commented Feb 19, 2015 at 0:28
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    @ykay I like this. But by this logic E.T. and Alf would be kosher too.
    – user6591
    Commented Feb 19, 2015 at 0:49
  • Valid points although regarding ET and Alf we can say אין הכי נמי :-) Commented Feb 19, 2015 at 8:49
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    If an ass 'fell from heaven' i may suspect a serious cargo malfunction from an airplane! .... or a trebuchet!
    – bondonk
    Commented Sep 23, 2015 at 20:56
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    @Dude שָׁמַיִם is often used throughout Tanakh to refer to the expanse of sky beyond earth within which the stars and various celestial objects exist. Genesis 1:14; 15:5; 15:17; 22:17, Deuteronomy 4:19, Judges 5:20, Jeremiah 8:2, etc. Commented Jan 10 at 14:30

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