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Comment by jrabone | Hacker News Reader

Hmmm. I don't know where they are in terms of sentience, but I kinda feel sorry for the jellyfish. It's the main reason I don't keep pets of any sort, but particularly fish. I love aquaria, but even the truly huge ones don't seem large enough - take the Lisbon Oceanário for example - hard not to feel sorry for that one Sunfish (maybe a metre across) just swimming in circles around a huge cylindrical tank.

Keeping cephalapods would be a great engineering challenge, in terms of what's necessary to make a viable habitat, but it seems so cruel given their apparent intelligence. Perhaps these things shouldn't be cheap?

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Most jellyfish are barely even animals, many are in fact several colonies of highly interdependent species that happen to work together in the form of a jellyfish. As long as you feed them and keep them warm/cold/lit/dark as appropriate to the species you have, it's no worse than having a pet plant.

Cephalapods on the other hand are significantly more intelligent that previously though, and therefore unless you could provide a sizable (like med-large house sized) enclosure for several of them... Don't keep cephalapods.

I'm a big environmentalist and supporter of animal rights. I originally wanted to be a marine biologist when I graduated college.

But I don't think keeping jellyfish in captivity is unethical. They're somewhere between a goldfish and a houseplant in terms of sentience. They have no central nervous system; just a loosely connected net of nerves that control their muscle contractions and very simple senses, like swimming towards light and migrating up in the water column at night and down during the day.

I would argue that it definitely is unethical to keep cephalapods in captivity unless they have a big tank and some sort of stimulation.

It's not only unethical for most people to keep cephalapods, but it's just a bad idea. They tend to escape from their habitats, some of them are extremely toxic, and almost all of them are very short-lived.

The current knowledge of jellyfish intelligence is "we've figured out they have memories." Jellyfish are extremely simple creatures; the "brighter" ones are known for their ability to avoid obstacles. [1] These are not particularly sentient creatures.

[1] Coates et al. 2006 "The spectral sensitivity of the lens eyes of a box jellyfish" JEB

It's relatively common for people to keep small reef aquaria without any fish at all. Just corals and other invertebrates like shrimp, snails, urchins, etc.

I keep some very small fish in my reef tank, but I find my non-fish livestock generally more compelling.

On the contrary – having them in close proximity might lead you to spend more time watching these puzzling and hauntingly beautiful creatures manifesting the same primordial intelligence out of which we evolved...

I think it's also important not to project our human minds onto jellyfish – it's very possible they are completely enlightened and are supposed to teach us something

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