It is written in the Torah: “You shall not plow with an ox and an ass together” (Deuteronomy 22:10). Just as the Torah forbade plowing with two different types of animals yoked together, probably because of the distress caused the animals by the mismatch, so is it forbidden to yoke together an ox and an ass for purposes of journeying or haulage.
One of the sages, Rabbi Rechavah, asked: is there a prohibition forbidding a carter from yoking a goat and a fish to his wagon? The fish would pull from the water and the goat from the ground. What are the issues in doubt? On the one hand, since the goat does not go into the water and the fish does not come up onto the ground, perhaps this is not considered together for purposes of mixed breeds. On the other hand, in reality he is driving his wagon using the fish and the goat together. (This question was not decided in the Talmud.)
(Babylonian Talmud, Tractate Bava Kamma 55a)
The Talmudic text:
Rechavah inquired: If a man drove [a wagon] by means of a goat and a fish together, what would be the legal position? Should we say that since a goat could not go down into the sea and a fish could not go up on to the dry land, no transgression has been committed, or do we say that after all they are now pulling together?