With the Piranha being designated a medium sized fish, and the Red-Bellied Piranha swimming around in schools of around 20 fish, that is quite a mass of fish.
So, how much does a Piranha weigh? In short, the Piranha genus contains as many as 60 species, varying in size and weight. The most common Piranha is the Red-Bellied Piranha and a typical adult fish would 12 to 14 inches and around 3kg (6.5 lb). In an aquarium they don’t grow quite as big, around 10 inches in length and a home aquarium Red-Bellied Piranha would be 2.5kg (5.5 lb). The very largest of the Piranhas, the black Piranha can grow to 18 to 24 inches which would be nearer the 5kg (11 lb) mark.
Introduction
One has to be quite careful when answering this question. Piranha are a genus of fish, within which there are between 40 and 60 species, depending upon how you classify them. The Pike Piranha (Serrasalmus elongatus) apparently maxes out at around 12 inches and in captivity gets nowhere near this size so it’s weight will be around 5 lbs.
However, the black Piranha (occasionally called Serrasalmus niger) is probably the biggest of the Piranha in the Amazon basin. They can average 16 inches, but grow larger. They also grow at a much slower rate than other Piranha and can take a decade to grow to their full size.
The Biggest Piranha – How Much Do Black Piranha Weigh?
The black Piranha (Serrasalmus rhombeus) is widespread throughout the Amazon basin. These are one of the largest Piranha species and can grow to 18 inches or more, although these are older fish and rare.
They are the slowest growing of all the Piranha species and a typical average might be around 12 to 14 inches in length. At that length the black Piranha would weigh around 3kg (6.5 lb).
The very biggest black Piranha is said to be around 24 inches long. That is a huge fish and would surely weigh around 5kg (11 lb).
A Typical Red-Bellied Piranha In An Aquarium
The Red-Bellied Piranha is easily the most common Piranha and an aquarium favorite due to its aggressive demeanour and its size for home enthusiasts.
It is commonly thought to be a carnivorous predator, but is in fact an omnivorous scavenger. Depicted through the very famous red bellies when they mature to adulthood.
They are said to be able to grow up to 20 inches but this would be very rare. At that size they would be approximately 4 kg (8.6 lb).
A much more typical and average Red-Bellied Piranha would be 12 to 14 inches and around 3kg (6.5 lb).
In a home aquarium they are often 2 to 3 inches shorter. A good fish in a spacious tank would be around 9 to 10 inches in length. At this length they weigh around 2.5kg (5.5 lb).
Conclusion
With up to 60 species of Piranha there is a great deal of variability in general weights for all the species. Some species are small, reaching 8 inches, while others are very large reaching 24 inches in length.
A very big fish might weigh around 5kg (11 lb).
Typically though, the Red-Bellied aquarium Piranha will be 9 to 10 inches in length and 2.5kg (5.5 lb).
