Piranhas in an aquarium
I wish to set up a Piranha aquarium. What are the basic care conditions?
I will split the answer into a number of different topics:
Setup: A very large aquarium (at least 1000 liters for 5 fish, preferably more) with sand bottom (the fish dig spawning pits) is required. The tank should be planted very abundantly and structured with roots. The lighting should be rather dim. Piranhas strongly tend to fright reactions in case of insufficient places to hide and too bright light, which may cause considerable injuries.
Food: In particular, whole fish (with skeleton, scales, head and guts) are advisable. If necessary, dead food fish can be wiggled back and forth with a pair of food pliers (not with the hand!) for triggering the hunting reflex. This especially applies for Piranhas that have not been living in an aquarium for a long time.
Water quality: Piranhas have an enormous digestion rate, but on the other hand do not tolerate water pollution well. A very powerful biofilter system, possibly distributed on several filters, and generous water changes are a precondition.
You have to be aware that it will beceome very difficult or even impossible to give away adult (over 30 cm!) Piranhas in case of problems or changes later on. You are thus binding yourself for a long time. Also, you must be aware that maintenance in a stocked aquarium is possible only with a couple of safety precautions. Piranhas may not be as aggressive as sometimes stated in the media - nevertheless they have teeth sharp as razor blades which they will use if they feel being attacked or threatened (not necessarily on purpose by the aquarist!).
Depending on where you live, it may not be legal to keep Piranhas at all. This is, for instance, the case in some states of the U.S.A. The reason behind this is that Piranhas might accidentally or on purpose get into public waters (rivers etc.) and endanger indigenous animals and, of course, people.
So please double check this with the local authorities in charge before getting into trouble!
In a nutshell: Piranhas are highly interesting fish, but you have to be aware that purchasing them includes long term consequences and may not be legal where you live.
Dr. Bodo Schnell