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?

Practical Fishkeeping (UK) - - Contents - WORDS: STEVE BAKER

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.

Essen­tail main­te­nence

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.

Black back­ground

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.

Black pi­ranha

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.

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