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i often see RBP in tanks with smaller fish, but when their is a larger feeder fish it will go after that? I always figured that other fishes but protected cats are going to get eatten.

So what is your question? I don't understand what you are trying to ask.

To answer the rephrased question(is it rephrased or am I really tired?)... It might be because the Pirhana does not see it as a meal because it is too small. That is my only guess.

Also, not everything that goes in with a pirhana gets eaten. There are fish that could try to bully the Pirhana (ie a big-ish cichlid) which would in theory survive...

This basically comes down to an energy equation, believe it or not.

How much energy will I expend in order to chase and capture this fish as a meal, and how much energy and nutrition will I gain from it if I catch it and eat it?

If a fish is too small, it's not worth going for unless you're a desperately hungry predator, because you may well expend more energy catching it than you get back after digesting it.

There's a certain minimum size of prey that guarantees, for any predator, that the resources expended in capturing that prey will be replaced upon digesting the prey. Anything over and above that contributes to the predator's own growth. The maximum size is determined by what the predator can safely engage as prey, and what the predator can swallow.

Of course, in the case of Red Bellied Piranhas, matters are complicated by the fact that in the wild, they hunt in packs. Which goes some way towards explaining how these fishes can attack and kill a 2,000 pound water buffalo! In the wild, they swim around in shoals numbering something around 250,000 individuals or thereabouts, and a quarter of a million Piranhas can inflict a LOT of damage in a short space of time on surprisingly large prey animals. However, they usually prefer to attack other fishes, and prefer to attack fishes that are small enough to swallow individually. Given a tight dry season, however, and being stuck in a slowly receding pool of water, once desperation sets in, a big shoal of Piranha, once it's members are hungry, will take the 2,000 pound water buffalo option if that makes itself available as a meal.

Then of course, Piranhas aren't at the top of the food chain. There are creatures that eat them in turnin the wild. Vampire Characins, Hydrolycus species, being a prime example. Several other Erythrinids such as Hopliac lacerdae will also eat Piranhas quite happily (and this beast is capable of amputating your forearm at the elbow joint if you let it ...). Then we have other larger fishes (I suspect a Pirahna won't put up much of a fight against being swallowed by a large Red Tailed Catfish or Piraiba), assorted fish eating birds (Herons etc) and Spectacled Cayman.

Also, chances are that Piranhas will be somewhat cautious when in the presence of groups of breeding Cichlids such as Green Terrors, that share their native waters. Green Terrors won't think twice about switching to "search and destroy" mode if they thing anything is threatening their young, and that includes Piranhas.

Nedless to say, though, all of this takes place in a huge system of watercourses with billions of gallons to play with. In an aquarium, I wouldn't put anything in with the Piranhas that wasn't intended as food, quite simply because the risk of calamity of one sort or another would always be present. In the case of smaller fishes, they would be permanently imperilled by the prospect of becoming lunch for the Piranhas, and in the case of something like Green Terrors, the scope for vicious internecine warfare to break out in the aquarium would be too great.

Hope this has been useful!


Panda Catfish fan and keeper/breeder since Christmas 2002

alright, my main question is where is the line between meal and tankmate?

the energy statement makes alot of sence, so i think i will use that in the everyday stocking with RBP

Meal versus tankmate? Depends on the size and hunger of the piranha, how the tank is set up, how large the tank is, and the speed and size of the other fish. The equation Cal mentioned about energy is a helpful rule, as sometimes predatory fish may not eat undersized prey.

My advice would be to never house piranha with fish which have value to the owner. It's all too likely that they will be killed, even if they're tough armor-plated catfish.

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And when he gets to Heaven, to Saint Peter he will tell: "One more Marine reporting, Sir! I've served my time in Hell."

there isnt a "LINE IN THE SAND" persay. if piranha are hungry enough they will attempt to take down larger prey than normal. but not before weeding out any sick, injured, or smaller fish. piranha can be surprising in what they will and wont go for, but Calilasseia was spot on with the "energy equation" theory. and its also true of all predators.

in a pirhana book, i remember that it could be possible to house protected catfish but also a group of cichlids? but of course the fishes should be well fed.

Well fed and in a really big tank!

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