I think there's a moral imperative not to kill animals for food that are above a certain level of intelligence; we can use intelligence level as a proxy for capability for suffering.

To take an example ranking of potential food animals: fish, chickens, cows, pigs, great apes, humans.

There's a question about where you draw the line, but most people agree there is one. Few people think it's OK to eat chimps.

It's not clear on this hierarchy where octopuses fit in.