I thought it should be mentioned that plecos can eat snails. We bought two snails, put them in our 200 liter tank, and went to eat dinner. When we came back, one of the snails had been sucked out of it's shell! The plecos had eaten dinner too, apparently. As we only had some goldfish in there, they must have been the culprits. The surviving snail is now living happily with a betta, in an 8 liter tank.
I've had one of these for about 8 years now. The only time it was ever aggressive was with my large angelfish, who was randomly attacking other fish. The pleco clamped on to its side and dragged it down into some grass...it took several minutes to beat him off the angel. As for hardiness, my mom somehow dropped a bottle of iodine in my tank one time, it killed all but the pleco in less than five minutes. The pleco held on for about three hours with his scales flaking off.
I would like to submit some interesting traits my fish named "Charlie" has. First of all Charlie is 48 cm long and I bought him only at maybe 4-5 cm. He is 10 years old and has been through a traumatic event by surving an explosion of the tank from my lamp falling onto the tank. It broke and he began to turn white but I saved him by air pump and trying to talk and calm him. We bonded during that time but he would not trust me for some time. He would always swim away from the glass when I feed him and now he blinks when you say hello and talk to him, plus he will swim over to you and blink at you. I also can pet Charlie he stays still with his dorsal fin down, calm. He also swims upside down. They do love algae tabs. He is beautiful and beats the zoos' fish. He is SuperPleco!
We've only had our Pleco for a short while, but what a fantastic fish! Similar to other's comments, our fish COMPLETELY cleaned our tank of algae in 2 days. It's great to watch it attack a piece of zucchini. But it's horribly shy, and will hide if it senses our presence outside the tank...unfortunately as it grows we'll either have to find it a new home or buy a bigger tank!
These fish are quite the surviors, my husband found 3 of them still in a tank after the store they were in was destroyed by Hurricane Charley. The store owners left many fish and reptiles behind, the stench was unreal, the workers were paid double just to go in. But these pleco's survived and are living in my home now.
The cat fish I have in India is now about 60 cm in length and is already 14 years old. As it had grown too big for the glass tank, I transfered it to a 1500 liter outdoor cement tank about 9 years back. The fish has stopped growing and hardly eats anything now, it is also very docile, but still alive and fine.