Triceratops and tropical fish - a question of intellect (theirs, not mine)

I'm probably going to get a reputation on the list in a minute if I keep using weird analogies between dinosaurs and totally unrelated animals (hey, technically chickens and ducks are related, just not to sauropods unless Larry Dunn, your student was right), but here goes anyway:
I was cleaning the build-up of algae off the front of my tropical fish tank last night, using the magnet, when I noticed all the fish had huddled themselves in groups, the largest of which, among a large stand of fake plants. In the middle of this group were all the young fish.
My question is this: If an animal like a fish that has by reputation a memory span of three seconds (don't know fishes well, don't know how true this is) can get it together enough to form a huddle of adults around the young, why not a triceratops herd as portrayed by Mark Hallet in one of his 1984 paintings (not sure if he proposed this idea too) and strongly doubted as a concept of behaviour by many members of the palaeontological community ever since? Don't get me wrong, I don't believe for one minute that the big fishes did this to defend the littluns, only that the little fish thought they had a better chance of surviving in between the biguns and perhaps the behaviour of Triceratops was carried out on the same motives. This would make the Mark Hallet version of events a little too regimental, but still…
Could this be a possibility or were there other grounds on which this claim was dismissed by the many experts who believed it wasn't possible? Did they already think up and discount or explain away this idea in any papers?