there have been recent studies on consciousness in animals. Initial results indicate it's possible. To what level who knows. Very much dependent on brain size, I'm Guessing. Note- not talking about intelligence. Animal intelligence is different. A horse is very smart for a horse-like animal. but don't expect it to add and subtract. Most animals can be target trained. I've seen them training spiny tailed lizards before. Snakes are highly intelligent; some prefer family structure. The bigger fish we keep are also very intelligent
When we have to sell animals, we have to be very careful. selling too many from a group will make the rest go off feed. So, yes, they actually do notice. usually not for long. And I'm sure you've seen videos of mama elephants mourning the loss of their calves before.
also have to remember, 30-40 tears ago it was controversial on whether fish actually feel pain or not