Fish are conscious creatures. There is no question about it. They are living, breathing just like you and me.
My bettas and plecos recognize me. My other fish (platies, danios) don't, but it's probably because they don't care to (and that's quite alright). I had 2 fiddle crabs - completely different personalities. I had 2 tiny ADF frogs, they both flinch at pain (I had to move them around between tanks).
All in all, I believe there is no question that fish (and other aquatics) are conscious, whether true or not. Leave the scientifically proven alone, because it is pretty much impossible to PROVE that even you and me are conscious. In my opinion, just knowing that they have a nervous system is enough to say they do feel pain.
this is the same half researched reasoning for the evangelical explination for man living with dinosaurs, very bad information, and science is EXACTLY that, only the things wich can be PROVEN.
you say your fish have a memory of you however for the most part they cant see you, depending on the thickness of your aquarium glass they cant see out of it at all.
another main point about pain is that without a memory pain is inconsequential, this is easily explained using the metaphor of a human male having a circumcision, while the act is phisically painful and the baby will cry, shortly after there is no memory of the event, this is due to an undeveloped brain at this point, however fish do not develop memories in the same sense that humans do because most memories rely on spoken language to describe said memory. fish do not comprehend language therefore have no refrence for pain. the reason an earthworm moves when you poke it is the basic fundamental of any living thing, INSTINCT, animals lives are completely dependant on instinct and our CONCIOUSNESS is what seperates us from them. I love my fish but I also understand that animals are subservant to humans, we are more developed and posess a level of intelligence that no animal could ever obtain.
just thought this discussion should have the real root discussed which is the fact that any form of euthinisation is simply that, killing the creature for its own benefit, this is to make us "the human owner" feel better about the situation, becasue when you think about the idea of keeping fish as pets, that alone is taking them out of their natural environment and placing them on display for asthetic quality, so the whiole humane portion of the discussion is kind of redundant, the humanity of keeping fish in a glass box is on par with that of smashing it with a mallet...
i do however agree that you should not flush a live fish down the toilet, and that is just a respect thing for me, in my climate the fish would die extremely quickly, however it seems just evil to simply flush it for no reason.