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Pacu - A Giant Characin of the Amazon

By David Marshall
Written for the October 2004 issue of the Ryedale Reporter, Ryedale Aquarist Society, England
Aquarticles

Background
In recent times a large number of dramatically written press reports, originating both in Europe and North America, have spoken of large pirhana species which uncaring pet keepers have deliberately released into various waterways once these fish have outgrown their aquaria. Many of these stories have turned out not to relate to the various pirhana species but to their close characin cousins the pacus.

Pacu in a Canadian pet store            Photo Howard Norfolk

In the case of the pirhana nature has shaped their lifestyle into one in which they form large schools, use their senses to locate weakened food items of living flesh (although some pirhana species specialise in eating the scales and/or fins of other fish species) that are attacked in a feeding frenzy and has endowed them with razor sharp teeth in order to tear through their prey with ease. In the case of the pacu nature took a completely different approach. These fish are very solitary in nature and have developed nasal flaps on the upper part of their snouts which allow them to detect their favourite food items of ripe fruits and berries. While the pirhana may eat all year round the pacus gorge themselves on fruit during the rainy season, which lasts from December through to May, building up enough fat reserves to see them through leaner times.

As the native peoples of South America, to where both pacu and pirhana are endemic, refer to a large number of fish as 'pacu' it is hard to establish exactly what the true pacu are but, while researching for the 'Tropical World' project, it appeared that six valid pacu species are recognised by the scientific community as follows :- Acnodon normani, Colosomma macropomum, Myleus pacu, Ossubtus xinguense, Piaractus brachypomus and Piaractus mesopotamicus.

Of these fish the two we are most likely to find in aquatic retail outlets, as a spin off from commercial farming for the table, are Colosomma macropomum (Black pacu, Black-finned pacu, Tambaqui) and Piaractus brachypomus (Red-bellied pacu. Many aquatic textbooks still refer to this fish as Colossoma bidens).

Human usage
The various pacu species first came to human attention due to their usage as a food item. Remember those wonderful television documentaries on how the first human settlers to North America came across huge herds of mammoth and how they devised various methods to hunt and capture this valuable food resource. I always imagine how early settlers to the Amazon basin first came across the Colosomma and Piaractus pacus in much the same way and with their large size and near body weights of 30kg it would be very difficult for these fish to hide their presence. Using sticks to imitate the sounds of falling fruits these subsistence fishermen brought pacu, or 'little river pigs' as they are known in Peru, to the water surface and then harpooned their victims with deadly accuracy.

Although this method is still used today, gill nets and other more sophisticated catching methods are now employed. Although commercial production of pacu now takes place, wild catches are still extremely important and Aquarticles visitors who were able to watch the recent satellite television series 'Jungle Hooks' will remember seeing large numbers of slabs in the Manaus fish market on which lay a huge number of variously sized pacu destined for the dinner table. Although the Amazon has continued to renew this resource, will the needs of an ever growing human population see wild populations of pacu go the same way as the mammoth?

As with all animals that are used for human consumption pacu find their meat available as 'choice cuts' with rib portions (that are said to be packed with firm, oily and juicy meat) and tail fillets the most popular consumer choice. Many South American travellers talk of this meat tasting like that of a chicken but perhaps the 'jungle effect' has an influence on taste buds as this is commonly spoken of as the taste of pirhana and Plecostomus meat also.

Now we all know that many modern medicines have their roots, literally speaking, in the Amazon rainforest but many moons ago a very astute Peruvian practitioner of local medicine found a use for the head of the Tambaqui that is still employed today. When boiled in water the head releases incredibly large quantities of fat. When left to cool this fat solidifies into what is known locally as caldo soup. When drunk this soup diverts a huge quantity of the human blood supply from brain to stomach thus enducing a state of narcolepsy that is used to cure insomnia. Although this may have short term benefits it makes you wonder what effect long term usage may have upon the users' brain?

At this point we should mention that the native peoples of South America respect the pacu to such an extent that many traditional stories, dances, festivals and costumes have been fashioned in their honour.

Today a new usage for the pacu has become very popular - sport fishing. Not only can you find specialist holidays to Bolivia that offer you a semi-wild environment into which to cast a line but the Far East tourist trade has taken note of their popularity introducing pacu into Thailand for the exact same reason.

My experiences with these fish
I never intended to keep a pacu in my fish house but two rescued Piaractus brachypomus came my way. The two fish had been kept as a 'novelty' in a large aquarium containing a variety of Rift Valley cichlids. The cichlids had shown them little respect so when they arrived with me their fins were shredded and they had small sore patches upon their bodies.

As these two fish were youngsters they were housed in an aquarium containing various Trichogaster and Loricarin species. The initial problem encountered came with feeding as the two pacu had only been fed on algae wafers and cichlid pellets so it took a lot of time before they would try the usual fare for pacu that includes pieces of carrot, cherry tomatoes, grapes, slices of apple and lettuce.

It did not take long for the two pacu to find their feet and begin recovery. Once I deduced that they were ready to make a move, after finding the Trichogaster with slight tears to their fins, they found themselves in an aquarium that was 2m long by 75cm wide by 75cm deep. What we must mention now is that pacus entering a new aquarium follow the tinfoil barb and Brochis catfish code of panic, so to counter any shock they must be treated very gently, allowing the water in their holding tub or large bag to be mixed with that of the aquarium before release. Thankfully I had no problems with my two.

As this aquarium already had a small resident population of various catfish species, a pair of lemon barb and a fully grown pair of red parrot cichlids there was no chance of silicone sealing items of décor, mainly large plastic plants (real plants become a snack item) and pieces of mopani wood, to the glass base and this would end-up causing me much work as almost everyday the two pacu, whether through intent or by accident, would uproot as much of these decorations as they could. For fun they loved the opportunity to splash water out of the aquarium, so regular water top-ups were always needed so as not to expose heating equipment, minimum water level safety marks etc.

The pH of the aquarium was 7 and the temperature was maintained at 26C. It became very important that the aquarium had a strong flow of air, as although nature has given the pacu a 'safety valve', in that the lower lip swells and forms a tunnel directing well oxygenated surface water over the gills, every time the air tubes became slightly blocked the two pacu would panic until this problem was solved. When pacu do panic the sight can be more frightening than the outcome. On the rare occasions when one or both went into shock I just left them alone and they quickly recovered.

At this point we must remember that there are known cases where pacu have taken their panic to the extreme, and have thus come flying through aquarium glass. Although their large weight and size makes it difficult for them to jump clear of an aquarium this action is not beyond their scope.

During the 3 years that the two pacu lived in this aquarium they never attempted to harm any of their companions. However there was no brotherly love between two of them and bouts of feuding, usually starting at feeding times, would suddenly start for no apparent reason. Thankfully this trouble was never bad enough to think of having to separate them although it did often lead to torn fins and abrasions but, remarkably, any damage quickly healed. Perhaps these fish are best kept in aquaria as a solitary specimen?

Jackie Goulder at Flamingo Land Zoo in North Yorkshire tells me that as pacu mature their aggressive nature increases and that they reach a stage were any new aquarium companions are not tolerated.

For more information on the aquarium care for and what is known of the breeding habits of the pacu species I refer visitors to my article in the October/November 2004 issue of the U.K. aquatic magazine 'Tropical World'.

I have to say that I did enjoy the company of the two pacu, watching them grow and change body colours is the real delight of keeping them, and I missed them after they left my fish house, but in all honesty would never keep these particular fish again. Should your aim of reading this article be in preparation towards keeping pacus please think extremely carefully before taking on such a responsibility, as much patience and more than a little luck is needed in order to cater for the needs of these particular fish, and as we saw at the beginning of our article, so many end up disposed of in ways they do not deserve.