I thought of this when reading the bird thread. I’ve never heard of a smart fish. I have never encountered a fish that behaved in any way I could recognize as intelligent. The memory span of a goldfish is only a few seconds; I don’t remember exactly how long, but it’s no more than five.
What is the smartest fish? Is any fish capable of learning? Is there any fish that doesn’t stare blankly all the time?
Apparently ocean sunfishes, aka molas, are very curious and approach boats with seeming interest. To me, this seems to infer intelligence, of a sort.
Fish are just below granite in the inteligence scale. 
Really, don´t expect an IQ past -10
I´d put them between insects and reptiles.
Also, it should be noted that squid and octopi demonstrate fairly high levels of intelligence, yet they are both more “primitive” than fish–which is to say, they evolved earlier than fish did.
Fish are actually a lot smarter than most people realize. I have kept fresh water fish for about 15 years now, and those in the Chiclid family seem to be fairly inteligent as far as fish go. Now there not going to fetch a stick or jump through hoops of fire, but there is method to their madness, although it may just be inherant.
They tend to be very territorial, especialy when breading, and will attack anything that gets in their space, including your arm. They will build rock wall fortifications to house themselves. They know it is feeding time when you approach, an obvious sign of learning, since they don’t do this when you first get them.
But you are correct, goldfish tend to be extremely stupid, and there is a wide scale as far as fish intelligence is concerned. You will see this when you put a gold fish, pirhana, and a chilid (such as a red devil) in the same tank. The pirhana, which is a mindless eating machine, will devour the gold fish rather quickly, granted the chiclid doesnt get it first. But even thought the pirahana could technicly eat the chiclid for lunch any day of the week, it will flee as the chiclid picks it apart, and eventualy wears it down and eats it.
Mmm… especial breaded fish…
Seriously tho, they build houses? I never in my life heard of a fish building anything. That’s pretty cool.
Wonder what a fish would build for a backyard pool.
Oh yes, octopi are a different thing… literally. 
Q.E.D.
Yes, from what I hear, octopi are especially intelligent. I heard someone who had a pet octopus claim that the octopus could even recognize him–FWIW.
Demigorgon.
Heh. Much wackiness is undertaken in the name of science. Thanks for the info.
Well the goldfish 3-second memory is obviously a crock… we all know that right? It’s very easy to get them to recognize feeding times, and to instill the fear of death into their memories - one of the most effective ways being letting them swim with the above mentioned pirahna but pulling them out once they get a few fins ripped off. Believe me, they don’t forget to freak out on seeing the pirahna when you put them back in with it a week later! But yeah, they ain’t the brightest fish out there.
Cichlids seem pretty quick, as do some larger catfish. Not that it’s all that great a sign of intelligence, but many types of danios and tetras can learn within a few seconds how to evade your net by charging through the 1/4" rip in it, darting straight for the one place you can’t reach, or by picking up evasive swimming patterns/routes that they’ll pull off several times in a row (to your utter frustration) until you learn to outsmart the fish. They will even see how the net moves as it comes after them and make a quick escape when you have to turn the net to get by a rock the same way every time. Just ask someone who tries to catch small fish with a net - there’s definately method to their madness, and the more times they escape, the harder it will get to catch them next time. In my past 13 years keeping fish, there was one time where I absolutely could not catch my 2 bloodfin tetras without pulling all the plants and draining the 65 gallon tank; and we’re talking about 2 hours worth of trying here. Got me so damn mad that I left them there and moved to the west coast without them!
As for actual studies investigating the intelligence of different fish, I don’t know of any… there’s just the generally recognized social behavior of cichlids and learning capability of cephalopods floating around out there.
There was a large mouth bass that was smart enough to spit out my lure just before I netted him. (I dislocated both my shoulders describing him to friends).
I can remember reading something in the early eighties about Mormyrids having the largest brains, but I can’t seem to find a useful link.
Here’s a picture and some general info, anyway:
http://www.scitoys.com/scitoys/scitoys/biology/electric_fish/electric_fish.html
Ok I’ll bite on this particular claim at fact. I had a Red Bellied Pirhanna for close to a decade. He died in 01’ I had him since college. My only reference to the above quote as being false, would be when a friend challenged me for months that his 6’inch chiclid would devour my smaller pirhanna. Finally, I said fine, I’ll bring my pirhanna over and we’ll see. make it in a week when both have not eaten… he got visibly excited and said “ok, yeah good idea”
I brought said pirhanna named Dilk Near (long story) over to his appartment. Dumped him in the tank. He promptly went into a corner and got his barings. Said cichlid darted around the opposite side of the tank. 6 college students all watched as said pirhanna waited for cichlid to attack. Turned, bit a dorsel, bit a pectoral, bit a gill, and proceeded to gorge himself on said cichlid. He didn’t eat after that for a month. I didn’t help dumbass friend clean his tank after either. :rolleyes:
But what exactly was said cichlid? Angel, Oscar, Discus, Jack Dempsey? What?
For those of us who aren’t familiar with chiclids, what are they, and what exactly do they do to other fish?
They belong to the Perciforme order (Perch-like fish), sub-order Labroidei, which as well as the cichlids includes wrasses, parrotfishes and damselfishes.
You’ve probably seen Angelfish, they’re a very common aquarium fish.
But some others can be large and (sometimes very) aggressive.
Here’s some photos of a nasty one.
Nice site Desmostylus .
Here’s another mean one.