Arapaima gigas

## About

An Arapaima.

***(Arapaima gigas)*** also more commonly known as the arapaima or pirarucu, is the largest extant species of freshwater fish. The body structure of the arapaima's body is elongated and its colouration is a dark grey or black colour which transitions into a mottled orange and red appearance towards the arapaima's caudal fins however, on some individuals these colours exceed towards the arapaima's pectoral fins. In the Brazilian indigenous language of Tupi, the arapaima is known as the pirarucu, roughly translating to 'red fish' in reference to this colouration. Two symmetrical characteristic fins appear on either side of the fish's caudal fins and are streaked also with reddish-orange scales. Across the face and head, the arapaima has a silverish grey colouration as well as a white colour on the mouth's underside. The characteristics of the arapaima's face also include characteristically small eyes and a slightly upturned snout. Arapaima have streamlined bodies that widen towards the caudal fins and bow upwards slightly in the mid-section. As the largest extant freshwater fish species, the arapaima is known to exceed 2m+ (6.5ft+) and grow to weigh 125kg+ (275lbs+) over the course of its 20 year lifespan.

## Diet

Arapaima are great predators however, do not rely completely on meat and are adaptable omnivores. Arapaima often eat mammals and bird species but are also known to consume fallen fruits and seeds as well as occasionally insects. As arapaima have specialised swim bladders, they can function regularly in low-oxygen zones, they catch other unspecialised fish species with relative ease. Whilst hunting arapaima employ the use of 'vacuuming' the area in front of their mouths in order to catch prey. The mouth of the arapaima is extremely specialised to this strategy, having many bony teeth, a bony tongue and specialised plates on the mouth's roof in order to pulverise their prey.

## Conservation Status

Though the IUCN sites that there are no immanent threats to this species, it is likely that a variety of threats exist, but are seldom-documented. All known threats to the arapaima involve human interference in the species natural habitat and population. Most commonly, the arapaima is threatened by overfishing, which is common place in the Amazon Basin. The overfishing impacting the species has been so impactful to the population of the species, the arapaima individuals that were once known to exceed 3m (9.8ft) and weigh up to 180kg (400lbs) are now either exceptionally rare, or completely extinct. The disappearance of the giant arapaima can be accustomed to the capture and fishing of arapaima as a food source and as a fishing trophy species. The arapaima's hide and body parts are often used in a variety of products, such as a food source however, their scales are also often turned into decorative jewelry or other accessories. A commercial species, the arapaima has been targeted profusely by predatory fishing industries. These practices have led to the arapaima becoming a regionally extinct species in portions of its Amazonian range. Further detriment to the arapaima's population comes in the form of accidental casualties. As fishermen find it harder and harder to catch prized mature arapaima, they will often resort to the use of gillnets in order to catch other species as a substitute. This method however, is extremely unsustainable and more often than not, leads to the accidental killing of juvenile arapaima. As arapaima have extremely specialised swim bladders which allow them to inhale air, they will often surface, which allows fishermen to easily hunt and kill them. In the species' Brazilian range, commercial fishing of it has been outlawed and although it has led to a resurgence in the arapaima population, specified regulation of the ban allows many to continue to fish the arapaima undetected. Some communities have began to impose their own laws surrounding the catching of the arapaima, enforcing bans on gillnet fishing and regulating minimum catch sizes for caught arapaima individuals, as to not exterminate populations of giant arapaima. Despite efforts made in these Amazonian populations, the arapaima was found to be extinct in 19% of the 81 communities survyed and depleted and overexploited in 57% and 17% respectively. Aquaculture and other fish farming method have also seemed to recover some of the arapaima population, specifically in Peru, where the species was declared 'no longer at risk of extinction', as aquaculture was incentivised to the general population rather than cocoa leaf cultivation in order to produce cocaine. In Brazil, WWF has worked with IBAMA in order to train local fishermen to accurately and sustainably regulate arapaima stocks. In addition to working as a sustainable practice, this educational program has also managed not to detriment the local fishing economy, thus benefiting all parties involved. Despite the threats listed above, the IUCN classes the species as data deficient due to its seldom-documentation.

## Range and Population

In its endemic/native range the arapaima is known to inhabit the countries of Brazil, Peru and Guyana. In these countries, the species inhabits riverine environments, such as the Amazon, Orinoco and Essequibo rivers however, they are adaptable and also inhabit flooded forests and floodplains in the Amazon Basin. The fish has recently becoming an invasive presence in Bolivia as of 1976. It is believed that this population was established due to a flood moving arapaima from Peruvian farms to Bolivian rivers. Through the effects of aquaculture farming, the arapaima has been introduced as an invasive species also to east and southeast Asia, where the species can be found in the countries of Thailand and Indonesia. It is unknown whether these populations where established purposefully or otherwise however, they still pose a threat to native riverine wildlife. The arapaima's population is unquantified and it is likely not stable due to previously stated factors.

## Behaviour

Due to the arapaima inhabiting areas of seasonal flooding and droughting, the species has evolved an extremely uncommon adaptation among fish. The swim bladder of the arapaima is extremely specialised and acts as a lung when the fish intakes oxygen from the surface. This allows the species to breathe outside of water, likely for a total of 24 hours, before succumbing to dehydration and suffocation. Though this adaptive measure assists the arapaima in many aspects, it leads to a detriment when being hunted by fishermen, as the arapaima must surface every 10-20 minutes. This is because the arapaima requires greater oxygen intake, due to its disproportionately small gills. Arapaima lay their eggs within the annual droughts of February-April and during these months, are more likely to employ their air-breathing capabilities, due to low water-level. During May-August, as water levels rise the arapaima will begin spawning. This spawning is well timed, as the juveniles will begin to thrive in the wet season. Arapaima are protective parents and mouth brooders. They will defend not only their eggs, but their offspring, even exuding a pheromone from their head in order to keep their young nearby.

### Relationship with Humans

Arapaima are often utilised for their scales and other products, which often leads to overfishing as mentioned above. The fish are also farmed commonly throughout both their native and introduced range, which has led to slightly more sustainable fishing practices.

## In Captivity

The arapaima is an extremely charismatic fish species and so the arapaima can be found in many institutes internationally. Facilities such as the Dallas World Aquarium, USA, Parc Zoologique de Paris, France and Leipzig Zoo, Germany are all examples of where arapaima are found in captivity.

## Sources

* IUCN Red List of Threatened Species - https://www.iucnredlist.org/species/1991/9110195
* Arapaima Gigas | Animal Diversity Web, University of Michigan Museum of Zoology - https://animaldiversity.org/accounts/Arapaima\_gigas/
* Arapaima Gigas | Wikipedia - https://en.wikipedia.org/wiki/Arapaima\_gigas
* Arapaima | Smithsonian's National Zoo & Conservation Biology Institute - https://nationalzoo.si.edu/animals/arapaima
* Amazon's Biggest Fish Faces Threat of Extinction | Live Science - https://www.livescience.com/47326-amazon-fish-faces-extinction.html
* The Amazon's Biggest Prehistoric Fish is Delicious and Dying | Vice - https://www.vice.com/en/article/3djgx3/the-amazons-biggest-prehistoric-fish-is-delicious-and-dying
* Arapaima: The Freshwater Giant | WWF-Brazil - https://www.wwf.org.br/?26210/Arapaima-the-freshwater-giant
* Arapaima | Maritime Logistics Professional - https://2015.maritimeprofessional.com/blogs/post/arapaima-13611