The most elegant study of fish pain that I've ever seen ... was done a few years ago by a biologist named Lynne Sneddon ... in the U.K. She used zebra fishes, which are very commonly used in research. And what they did was they put a group of zebra fishes — I don't remember how many, perhaps 30 — in a complex tank that had two chambers. One chamber was enriched, it had rocks and vegetation, and the other chamber was barren. It was open. You can probably guess which chamber these fishes spent all their time in — it was the enriched one. Fishes like places to hide, they like stimulation in their environments.
And then they injected the fishes either with one of two things. One was with an acid solution, which is known to be caustic and presumably painful to these fishes, if they can feel pain. And then the other ... half of the fishes were randomly selected; [they] were injected with saline, which causes just the pierce of the needle and then the pain is not going to be lasting, because it's not acidic. And then they watched to see how they behaved, and they all remained swimming in the enriched tank. And then they dissolved a painkiller solution in the barren, undesirable chamber of this complex tank. And lo and behold, some of the fishes then started to migrate across and swim and hang out in that normally undesirable tank, and it was only the ones injected with the acid, and not the ones injected with the saline. I find that a pretty convincing demonstration of pain in fishes.
What animal sentience means
Sentience is like pregnancy. You're either pregnant or you're not, you're either sentient or you're not. And if an animal is sentient, which means some kind of conscious awareness, but particularly the capacity to feel pain, and, I would say, by extension, to feel pleasure, then, to me, that means that animal has moral traction, or it should have moral traction — that the animal is deserving of consideration of others. Because that animal can have a good day and a bad day and can have good or bad things happen to them. And that, as I say, is the bedrock of ethics.
On some reef fish appearing to recognize individual divers
There was a new study ... showing individual recognition of human faces by fishes. So they probably do recognize individual divers. They come up to be stroked. It is almost like a dog. I don't know if they roll over to have their belly petted, though some sharks will be sent into what looks like a euphoric state when they have their bellies rubbed.
On how fish use a 'lateral line' to sense water pressure and navigate at night
[Fish] have a couple of other pretty neat senses that are worth mentioning. One is a sense of water pressure or movement in the water that's very acute, thanks to a lateral line.
We're talking about bony fishes now, not the sharks and rays. ... The bony fishes have a lateral line. You may notice a dark row of scales along the center line of a bony fish, and that's actually the shadow cast by these specialized scales. Because there's a depression in each one, and in that depression are specialized little cup-like chambers with gel in them and little hairs that stick out and they detect pressure changes. So it's very useful for navigating at night, for avoiding dangerous things in limited vision conditions and that sort of thing.
On the electrical senses that some fish have
Some fishes, including sharks and I think rays as well, are electro-receptive. They can detect electrical signals from other organisms.
There's also electro-producing fishes. The knife-fishes of South America and the elephant-nose fishes ... they're both electric-producing, so they have E.O.Ds, which are electric organ discharges, and they use those as communication signals, and they communicate in some pretty cool ways. They will change their own frequency if they're swimming by another fish with a similar frequency, so they don't jam and confuse each other. They also show deference by shutting of their E.O.Ds when they're passing by a territory holder. You don't want to piss off the territory holder, so it's probably better to go "silent" during that time.
The perceptions and sensory abilities of fish, they're the product of over 400 million years of evolution, so it might not surprise us that they've got some pretty cool ways of sensing their environments.
On fish using flatulence as a means of communication
There is one really curious example involving herrings that I can't resist mentioning. I think if you were to come up with a phrase that best captures it, at least a delicate phrase, "flatulent communication" would be perhaps the right phrase. They live in big schools and they omit gasses from the anus in large numbers, and it makes a sound. And they appear to use this as a communication device to maybe signal to others that it's time we moved up or down in the water column, because it's that time of day when the predators are coming out and this sort of thing. The researchers who studied it use the more technical term "Frequent Repetitive Ticks." and I'll leave it to the listener to make an acronym out of that, which is quite appropriate to the behavior.
On the aquarium trade and the popularity of the blue tang, the fish featured in the movie Finding Dory
Some of the methods to catch [blue tang] are pretty awful. Cyanide poisoning, which often kills many of the fishes being targeted, or ones not being targeted, and explosive devices are sometimes used. And then you have the vicissitudes of transport, where they're shipped over continents and the mortality rates are quite high. ...