Plutarch Quaestiones Convivales 8.8.3

[3] Sylla commended this discourse, and added concerning the Pythagoreans, that they then chiefly tasted flesh when they sacrificed to the Gods. Now no fish is ever offered in sacrifice. I, after they had done, said that many, both philosophers and unlearned, considering with how many good things it furnisheth and makes our life more comfortable, take the sea’s part against the Egyptians. But that the Pythagoreans should abstain from fish because they are not of the same kind, is ridiculous and absurd; nay, to butcher and feed on other animals, because they bear a nearer relation to us, would be a most inhuman and Cyclopean return. And they say that Pythagoras bought a draught of fishes, and presently commanded the fishers to let them all out of the net; and this shows that he did not hate or not mind fishes, as things of another kind and destructive to man, but that they were his dearly beloved creatures, since he paid a ransom for their freedom.

Therefore the tenderness and humanity of those philosophers suggest a quite contrary reason, and I am apt to believe that they spare fishes to instruct men, or to accustom themselves to acts of justice; for other creatures generally give men cause to afflict them, but fishes neither do nor are capable of doing us harm. And it is easy to show, both from the writings and religion of the ancients, that they thought it a great sin not only to eat but to kill an animal that did them no harm. But afterwards, being necessitated by the spreading multitude of men, and commanded (as they say) by the Delphic oracle to prevent the total decay of corn and fruit, they began to sacrifice, yet they were so disturbed and concerned at the action, that they called it ἔρδειν and ῥέζειν ( to do), as if they did some strange thing in killing an animal; and they are very careful not to kill the beast before the wine has been thrown upon his head and he nods in token of consent. So very cautious are they of injustice. And not to mention other considerations, were no chickens (for instance) or hares killed, in a short time they would so increase that there could be no living. And now it would be a very hard matter to put down the eating of flesh, which necessity first introduced, since pleasure and luxury hath espoused it. But the water animals neither consuming any part of our air or water, or devouring the fruit, but as it were encompassed by another world, and having their own proper bounds, which it is death for them to pass, they afford our belly no pretence at all for their destruction; and therefore to catch or be greedy after fish is plain deliciousness and luxury, which upon no just reason disturb the sea and dive into the deep. For we cannot call the mullet corn-destroying, the trout grape-eating, nor the barbel or sea-pike seed-gathering, as we do some land-animals, signifying their hurtfulness by these epithets. Nay, those little mischiefs which we complain of in these house-creatures, a weasel or fly, none can justly lay upon the greatest fish. Therefore the Pythagoreans, confining themselves not only by the law which forbids them to injure men, but also by Nature, which commands them to do violence to nothing, fed on fish very little, or rather not at all. But suppose there were no injustice in this case, yet to delight in fish would argue daintiness and luxury; because they are such costly and unnecessary diet. Therefore Homer doth not only make the Greeks eat no fish whilst encamped near the Hellespont, but he mentions not any sea-provision that the dissolute Phaeacians or luxurious wooers had, though both islanders. And Ulysses’s mates, though they sailed over so much sea, as long as they had any provision left, never let down a hook or net. a little before they fell upon the oxen of the Sun, they caught fish, not to please their wanton appetite, but to satisfy their hunger,— The same necessity therefore made them catch fish and devour the oxen of the Sun. Therefore not only among the Egyptians and Syrians, but Greeks too, to abstain from fish was a piece of sanctity, they avoiding (as I think) a superfluous curiosity in diet, as well as being just.