When the best is not available, an inferior substitute will do. SOURCE: Bernstein, Jüdische Sprichwörter und Redensarten. The odd juxtaposition in this saying comes from splicing together a Talmudic aphorism (in Hebrew) and a Russian proverb (in Yiddish):
B'makom she-ein anashim, hishtadel lih'yot ish. | .במקום שאין אנשים השתדל להיות איש
In a place where there are no worthy men, strive to be worthy.
Pirkei Avot 2:6
На безрыбье и рак рыба. | If there is no fish, even crawfish is fish.
The two references are playfully linked through the rhyme of ish ("man" in Hebrew) and fish ("fish" in Yiddish). As Benjamin Harshav explains in The Meaning of Yiddish, the Yiddish proverb substitutes herring, which is kosher, for the unkosher crawfish or crab in the Russian proverb, but both species are considered "poor man's food." Coarse, everyday herring, writes Harshav, is not considered real fish because it cannot be used to make gefilte fish for the Sabbath. But if the ideal is not available, we make do with whatever we can get. Harshav notes that this expression is often used by a self-effacing speaker as if to say, "In the absence of a worthy man, I will be the substitute."
A simpler version of the Yiddish saying omits the Talmudic reference and parallels the Russian proverb:
Az s'iz nito keyn fish iz hering oykh fish. | .אַז ס'איז ניטאָ קיין פֿיש איז הערינג אויך פֿיש
If there is no fish, even herring is fish.
SOURCE: Stutchkoff, Der Oytser fun der Yidisher Shprakh