BITING FOR THEIR LIFE
The world can’t make its mind up about this South American shoaling predator. What’s the truth? Is it a cold-blooded predator or a much-misunderstood softy?
Its reputation precedes it, but is the Piranha an aggressive, cold-blooded predator or a much misunderstood softy?
WELL, IT’S a cold-blooded predator, literally. And it’s mostly misunderstood. But I don’t think I’ll go so far as to say it’s a softy. While the films ‘Piranha’ (1978), ‘Piranha 2’ (1981) and ‘Piranha 3D’ (2010) depicted our fishy friends as the most organised, hyper-aggressive killing machines freshwater has ever seen, now we’re bombarded by documentaries aiming to redress the balance. I’ve seen a presenter wade into a swimming pool with a shoal of piranha, and jumping into a river seconds after catching them to show they’re not just mindless killers. So should we ignore the films?
Nothing to fear? At your peril! The name ‘piranha’ means ‘tooth fish’ in the Brazilian language Tupi, and while few of us will come into contact with these feisty fish in the wild, if you do, approach with real care. There are many, many fishermen in South America with bits of fingers or toes missing, and even more with scars to prove these fish demand our respect.
The largest species – the Black piranha, Serrasalmus rhombeus – has a bite force of more than 32kg. That’s from a fish whose record catch weight is 3.83kg, putting it ahead of the Great white shark in jaw strength comparative to body mass. Their teeth are made for cutting – each tooth is only about 4mm long, but they’re sharp as razors and fit snugly, interlocking to slice through flesh and steal a piece before moving on to let another fish take a bite.
It’s not unusual to find piranhas with missing teeth. Several times over their life, they replace any missing tricuspid (threepointed) teeth, but rather than do it individually,
like sharks, they do it by quarters, growing and replacing all the teeth on one side of a jaw at a time. These replacements are ready developed in the jaw, waiting for when they’re needed.
As with most opposing views, the truth about piranha behaviour lies somewhere in the middle. They are ferocious, voracious predators, who can strip all the flesh from a cow’s carcass in minutes, but at the same time, the diet of the Red-bellied piranha, Pygocentrus
nattereri, is largely made up of aquatic invertebrates, crustaceans, insects, seeds, nuts and fruits.
The classic Piranha ‘feeding frenzy’ comes down to feeding pressure. Through the best part of the year, Red-bellies swim in small shoals. Contrary to popular belief, they don’t shoal as an aggressive tactic to overcome prey, but rather for safety from the likes of giant river otters, caiman, river dolphins, eagles and predatory fish species.
A shoal comprises around 20 individuals. Food is plentiful and aggression levels are low, so you
won’t encounter frenzied feeding in these conditions. When water levels get lower, and large numbers of fish are brought together in everdecreasing streams and lakes towards the end of the dry season, feeding pressures are heightened. With less
They don’t shoal as an aggressive tactic, but rather shoal for safety from the likes of giant river otters
space to spread out, shoals of piranhas meet shoals of hundreds of other species, and where mass shoals of piranhas congregate, the feeding pressure results in the annihilation of meaty passers-by, dead or alive.
You’ll never see this in captive fish. For a start, there just isn’t same pressure to feed. You’ll never have enough fish in a tank to create such pressures without running into serious water quality issues, and if you limit food to heighten aggression, you’ll just end up with your piranhas tucking in to each other.
Like other large fish, piranhas need clean, healthy water conditions, but produce a lot of waste to foul their tank. With no suitable tankmates to hoover up excess food, it’s a huge job for the aquarist, necessitating big, regular water changes and waste removal. It also puts the emphasis on providing strong filtration, both mechanically and biologically. Most keepers prefer to use two large external filters rather than one massive one; not only does this safeguard in case one filter fails, but two lots of flow makes it easier to avoid dead spots. It’s ideal if heating is integrated with the filtration, either by using in-line heaters or a thermofilter – this also provides peace of mind that there are no power cables in the water to be chomped through. Lighting is up to the keeper. Although piranhas get stressed in a sparse tank, they aren’t upset by strong lighting, so whether you want dull illumination or a brightly lit tank, your fish should be happy.
When it comes to substrate, experienced keepers tend to go one of two ways – either a bare base or black sand/gravel.
Bare glass is far easier to keep clean but the fishes’ colours tend to suffer. This can be limited by painting the base black (underneath) but the reflective glass is still likely to subdue colours slightly. A black substrate, be it sand or gravel, will help show off your fish, and can be further enhanced by strong, green plant growth. If you fancy a more subtle, atmospheric tank, go for a few large pieces of wood, sand, leaf litter and low light levels. A couple of spotlights to create shafts of light will intensify the mood.
The next question is how many fish to keep. Red-bellies can either be kept singly or in groups of five or more. On their own, they are still active and show confidence and will need a minimum 200 l tank. The larger S. rhombeus is a solitary fish in the wild, but a solo specimen still requires a tank of 500 l, ideally 2m or more in length.
In numbers, Red-bellies want about 100 l each, so a 150x60x60cm tank would be a basic set-up for a
small shoal of five, but you can really see the bonus of a larger tank with more fish. I’ve seen a few BIG piranha displays, 1,000-1,300 l sort of size and the result is stunning.
Red-bellied piranhas are widely distributed over much of South America. Since 1997, ichthyologists have classed Pygocentrus ternetzi (described by Steindachner 1908) as a southern strain of P. nattereri (Fink and Zelditch couldn’t find reliableenough characteristics to define a species), labelling P. ternetzi as a nonlinear cline (non-sequential features) as they differ in body shape and have more of a yellow belly than red. These fish often go under the trade name ‘Yellow emperor piranha’ in shops.
P. nattereri are found throughout the Amazon basin including Brazil, Bolivia, Colombia, Ecuador and Peru. They’re also found in Rio Essequibo in Guyana and Venezuela, Rio Paraná in Brazil, Paraguay and Argentina, Rio Uruguay in Brazil, Uruguay and Argentina, and among coastal drains in north-east Brazil and the Guianas.
The Red-bellies don’t restrict themselves to particular habitat
Red-bellies are found in major river channels, tributaries, and flood, oxbow and man-made dam lakes
types. They are found in major river channels, major and minor tributaries, temporary flood lakes, oxbow lakes and man-made dam lakes. They prefer deeper waters, but aren’t fussed whether they’re white, clear or blackwater conditions.
Females generally grow larger than males and have a rounder body shape when mature, but the fish can’t be sexed as juveniles. This throws a fly in the ointment if you’re looking to keep a group, as males become territorial as they mature. A tank of mature males generally ends up with individual fish almost motionless in their part of the tank, and not the interactive shoal their keeper desires.
Evidence suggests that the Black piranha, Serrasalmus rhombeus, is endemic to Guyana. However, it’s officially been recorded as coming from Guyana, Venezuela, Suriname, French Guiana, Colombia, Ecuador, Peru, Bolivia and Brazil. It’s possible that sightings outside Guyana have been cases of mistaken identity as identification of certain species is challenging. Some expect S. hollandi and Pristoprycon aureus to be declared synonymous with
S. rhombeus at some point. The red eye is a good identifying mark and gives rise to an alternative common name, the Redeye piranha, but the red eye isn’t developed in juveniles. Add to this the fact that geographical forms exist, there are several synonyms (such as S. niger), and confusion with common names ‘Black’, ‘white’ and ‘redeye’ all being used, and you can see the issues.
Black Piranhas shoal in shallow, well-vegetated streams as youngsters, then become solitary as they age and mature, moving to deep areas of major rivers. Like the Red-belly,
S. rhombeus adapts easily to different water types and is happy in steadily flowing water or at the edge of rapids – a favoured hunting ground. Food items include fish, crabs, insects, small mammals and chunks of flesh and fin bitten from big fish.
Some keepers do mix them with other Piranhas, but there’s always a risk involved. Much safer to keep a lone fish and revel in that singular character. Despite their fearsome reputation, they can make a pretty good ‘pet’.
BELOW: A mature Black piranha showing red eyes.
LEFT: The revered Redbellied piranha. At certain times of the year, Red-bellies congregate in large numbers.
BELOW: Piranhas are prey themselves.
BELOW: An immature Black piranha lacking colour in the eyes.