I like to think my fish have some smarts, on a certain level. But I can see as well how some see it as simply being conditioned to respond to certain stimuli. We're all allowed our own opinions here, there's no wrong or right. But think about it from the perspective for a minute. You say your fish reacts to you one way, but different to a total stranger. Maybe it doesn't recognize you the way people do, but maybe it can detect subtle signs its the bringer of food, such as your voice or some other more subtle sign (vibrations caused by your distinct movements or sounds perhaps..). I doubt they can see you the same way a person does, not a fish anatomy expert but somehow I don't think they have the same acute vision we do. So anyway, it comes to associate this sound, this vibration, whatever, this stimuli, with being fed. So whenever you come near the tank, the fish react, whether they're being fed or not. And they may associate the distinct sounds of a certain type of fish food from others. I really don't know, just throwing out ideas here to support both sides of the argument.
I wouldn't say fish are dumb though, far from it. They learn quickly what the signs are they are about to be fed, they seem to learn that the net is a bad scary thing. Okay, so those that continously pick up poo only to spit it back out, do make you question their intelligence sometimes....
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(Then again, maybe its their subtle way of telling you to clean up the tank. Ah-ha, intelligence rearing its ugly head? Fish wrapping us around their little fins, making us their personal slaves? Hmmmmmm
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) And I do believe that some fish have the capacity for learning beyond the basic instinctual things (like hide or flee from danger). You can train some fish to do tricks. Some fish, such as Oscars, love to "play" with toys and benefit from the stimuli. That to me suggests a somewhat higher level of intelligence than say a neon might have, it goes beyond the instinct to just exist. And sometimes, I even swear fish know just how to push my buttons when I'm trying to clean the tank (darn mollies, always nibbling on my fingers and scaring the crap out of me when I'm not expecting it....
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). Bettas are one fish that I do feel exhibit a higher level of intelligence as well. They respond to training beyond just "its time eat". Maybe it has something to do with not being a schooling fish but rather a more solitary species that allows them to develop a greater capacity for learning.............
Just my long-winded two cents.