Here is a photo of my first fish tank ever. It was a 10 gallon tank with two red belly piranhas, one tiger Oscar fish, one blue African Ciclid, a pleco and a blue lobster (actually a crayfish).
One piranha killed the other, than proceeded to kill the blue Ciclid. I added a second pleco to the tank, and the Yellow African Ciclid on the photo. Having two plecos seems to make them more active as they compete for food. The Ciclic is highly territorial and chased the piranha around all day, making it less aggressive towards the oscar, which was getting fins bitten off all the time.
The piranha then proceeded to kill one of the plecos. I got an Albino pleco to take its place, and planted two Amazon Swordplants to give the piranhas hiding places. I bought a second piranha, which became food within a couple of minutes… I also bought a flying fox, which was supposed to be O.K. with piranhas… That “disappeared” completely overnight. Guess you can’t believe everything you read…
A more recent photo of my fish tank shows how quickly the oscar grew. The lobster shedded its exoskeleton twice and grew a bit also, along with the piranha. All the fish were moved to a 20 gallon tank. I added a second, smaller Oscar to the tank, and a Pacu, which was supposed to become food. The piranhas would not eat the Pacu so I gave it away, along with the yellow ciclid which was becoming a nuisance as it harrassed the piranha all day. A week later the piranha killed and ate more than half of the Oscar fish, which was at least 5 times bigger then it! That was a real shame because the Oscar was one of my favorite fish: It would jump out of the water to grab food from my hand, and let me pet it after it was done eating.
Here is a close up of the Piranha. Notice the teeth it has. I one time hand fed it by holding a worm above the surface of the tank, but I never tried that again after I saw what its teeth did to a fish 5 times its size. You can also see a photo of the blue lobster, climbing on the heater. The piranha recently tore the lobster to pieces, consuming every last bit of flesh in less than an hour. It was quite upsetting as this was actually rather expensive! It also killed a 3rd piranha I put in there which was slightly larger than itself. To date, this piranha has consumed (intentionally or not): A frog, an Oscar Fish, a crayfish, a flying fox, a pleco, a ciclid, 3 other piranhas, a beta fish, tetras, and countless goldfish. I normally feed it carnivore food pellets, worms, or feeder goldfish. It puts on a real show when it is eating, but is quite shy and quiet during most of the day. I suspect that this is a Red Throated piranha (Serrasalmus spilopleura), as opposed to the common red belly (Pygocentrus Natteri) found in most fish tanks; its teeth are visible and it is extremely aggressive, even towards other piranhas.