Based on fish in general, not smart. Some species are fairly smart though. Like Largemouth Bass, which once caught on a specific lure or fly, will never hit one again. Years ago, I basically trained an entire small lake full of Bass to never hit a white spinnerbait. Musky are the same not only turning down the lure thereafter, but generally will not return to the spot it was hooked, associating it with a bad experiance and will not venture that shallow again as a rule. Then you have fish like Goldfish which have been scientifically shown to have a short term memory shorter than a minute.....by nearly a minute. It varies species to species. Walleye, despite their reputation as a smart and wary fish, are dumber than a bag of hammers. This is a you tube video where I caught the same large Walleye twice. 15 days apart with the same fly, in the same spot. It was caught at least once in between the two times I caught it, as I hand land them and it's fins are split up the second time, from being in a net.