The Amazon is home to so many amazing forms of life, including one of the largest freshwater fish. The arapaima, or piracuru, are giants of the Amazon’s waters which we’ll look at today. Looking prehistoric, they are one of the many wonders of South American fauna.
Taxonomy and Evolution
For a long time it was believed that there was only one species of arapaima, Arapaima gigas, as two other species had hardly been sighted since the 1800s. In 2013 a new species known as the slender arapaima was officially named by science, and since then a fifth species has potentially been identified which has informally been called A. arapaima. This means that we may have four or five species of arapaima, but as A. gigas is the best known we will largely discuss this species today. Araipama belong to an order of fish known as Osteoglossiformes, an order first appearing in the Jurassic and are natives of Africa’s, South America’s, Australia’, and southern Asia’s freshwater. These continents were once close together, especially South America and Africa, and it is no coincidence that the closest relative of the arapaima is an African fish. The genus first appears in the fossil record 23 million years ago in what is now Colombia which makes it one of the oldest genus of freshwater fish that still exists.
Biology and Behaviour
Arapaima are some of the largest freshwater fish in the world reaching lengths of 2.5 metres (15 feet) and a weight of 200 kilograms (440 pounds). This puts them just below some true river monsters like the Mekong river catfish, beluga sturgeon, and giant freshwater stingray. A streamlined black body covered in very strong scales, a copperish upturned head, and a red tail they are instantly recognisable. In fact, their red tail, and their red flesh, earned them the name piracuru in the Tupi language which means ‘red fish’. Something very unique with the arapaima is that the adults do not have gills and instead swim close to the surface of the water taking loud gulps of air every 10 to 20 minutes. This isn’t the most efficient system considering far more active dolphins can hold their breath for the same amount of time. A modified swim bladder moves into the mouth while it takes a gulp serves as a makeshift lung. The ever changing path of the Amazon river and its tributaries can potentially leave animals trapped in small pools, which are at risk of drying out, so the swim bladder-cum-lung arapaima’s possess helps it adapt to an ever changing ecosystem. River waters can also spread over decaying vegetation which strips available oxygen from the water, so the ability to breathe air gives arapaima an advantage. Through this, arapaima can survive out of the water for an entire day!
Arapaima are reliant on their changing rivers and lakes for reproduction. When the rivers overflow the arapaima spread out, taking advantage of the low oxygenated water as it covers the decaying vegetation. When the waters recede, February and March, females use their fins to dig a small burrow in the mud which she then lays thousands of eggs. When the wet season returns September through December the young hatch out of their eggs. For the next three months the father will guard his offspring, and will even suck them into his mouth to transport them to a place of safety if predators get too near. They do grow quickly, and have some of the highest growth rates in all fish. At around the age of 4 or 5 the young reach maturity, and can potentially live for 20 years.
Before we move on we can quickly discuss how arapaima eat. Their slightly upturned jaw is the key. While capable of small bursts of speed arapaima are slow swimming fish but they can extend the front of their jaws and suck water into them. This creates a vacuum that pulls food into the giant jaws. When in the jaw sharp teeth and even the tongue help break up food which can then be swallowed.
Distribution and Habitat
Arapaima are found in the Amazon river basin as well as some of its tributaries and nearby lakes. Specifically, they are found in the Guyanese and Brazilian sections of the Amazon, although unexpected flooding has sometimes allowed them to also spread to Peru and Bolivia. When this happens they become incredibly invasive for Bolivia’s ecosystem. While not all of the Amazon river is low in oxygen, arapaima prefer the low oxygen bodies of water as their air gulping gives them an advantage due to a lack of predators and competition.
Diet and Predators
Arapaima are generalists and will eat anything that they can suck into their jaws. They primarily eat fish and insects but are not adverse to fruit. Amphibians, reptiles, and birds near the surface can also be eaten, and they are capable of short bursts of speed to launch themselves out of the water to catch even small monkeys. Due to their size and hard scales adult arapaima have very few natural predators with caimans, jaguars, and humans being the main predators. Indigenous peoples in the Amazon have hunted arapaima for thousands of years as their large size means lots of meat can be taken from them, their scales make good decoration, and their surface swimming making them an easy target. Apparently arapaima flesh is very tasty. Young arapaima have far more predators including snakes, piranha, birds, and even river dolphins.
Conservation and Threats
The IUCN has not evaluated any of the four confirmed arapaima species, mainly due to how dense the Amazon is which makes research difficult. Arapaima numbers have certainly been threatened since the 1950s. Increased exploitation of the Amazon has led to pollution of the waters and an increase in hunting the fish. Nicknamed the ‘Cod of the Amazon’ arapaima were essential protein sources for many communities in the Amazon, new and old, which had managed to extirpate arapaima from several tributaries. Luckily, the Guyanese and Brazilian governments managed to implement quotas about when and where arapaima could be fished, with the Brazilian initiatives working directly with indigenous communities who know how to best manage fish numbers. However, time will tell whether arapaima can make a come back.
Bibliography:
- ‘Arapaima’, National Geographic, [Accessed 13/06/2023]
- Brian Clark Howard, ‘New Giant, Air-Breathing Fish Discovered’, National Geographic, (01/12/2016), [Accessed 15/06/2023]
- Cleber J. R. Alho, Roberto E. Reis and Pedro P. U. Aquino, ‘Amazonian freshwater habitats experiencing environmental and socioeconomic threats affecting subsistence fisheries’, Ambio, 44:5, (2015), 412-425
- Kang Du, Sven Wuertz, Mateus Adolfi, Susanne Kneitz, Matthias Stöck, Marcos Oliveira, Rafael Nóbrega, Jenny Ormanns, Werner Kloas, Romain Feron, Christophe Klopp, Hugues Parrinello, Laurent Journot, Shunping He, John Postlethwait, Axel Meyer, Yann Guiguen, and Manfred Schartl, ‘The genome of the arapaima (Arapaima gigas) provides insights into gigantism, fast growth and chromosomal sex determination system’, Scientific Reports, 9:5293, (2019)
- Joseph Nelson, Terry Grande, and Mark Wilson, Fishes of the World, Fifth Edition, (Hoboken: Wiley, 2016)
- John Lundberg and Barry Chernoff, ‘A Miocene Fossil of the Amazonian Fish Arapaima (Teleostei, Arapaimidae) from the Magdalena River Region of Colombia–Biogeographic and Evolutionary Implications’, Biotropica, 24:1, (1992), 2-14
- ‘Arapaima’, Smithsonian National Zoo, [Accessed 17/06/2023]
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