In the depths of the Amazon River resides a true aquatic giant: the Arapaima. This magnificent creature, also known as the “Giant of the Amazon,” is the largest freshwater fish in the world and captures the awe and curiosity of both scientists and nature enthusiasts.
With its long torpedo-shaped body, distinctive scales, and reputation for reaching lengths of up to 3 meters (10 feet), the Arapaima, also known as pirarucu or paiche, has rightfully earned its majestic status. However, it is also important to highlight its significance for the aquaculture industry.
In this article, we will delve into the world of the Arapaima, exploring its notable characteristics, extraordinary behavior, fish farming, and the use of byproducts (scales, skin) from processing.
Taxonomy and Physical Characteristics of the Arapaima
The Arapaima, also known as Pirarucu or paiche, is a freshwater fish native to the Amazon that holds the title of one of the largest in the world.
Domain: Eukaryota
Animal Kingdom
Phylum: Chordata
Class: Actinopterygii
Order: Osteoglossiformes
Family: Osteoglossidae
Subfamily: Arapaiminae
Genus: Arapaima
Species: Arapaima gigas, A. map, A. agassizii, A. arapaima, and A. leptosome.
Common names in Spanish: Arapaima (Colombia, Ecuador, Venezuela), paiche (Peru), de-chi (Guiana), pirarucu, and “Amazon cod” (Brazil).
The paiche can reach up to 3 meters in length, weigh over 200 kilograms (400 pounds), and live for more than 20 years in the wild. Its elongated and robust body is covered with thick, shiny scales, olive green on the back and reddish-orange on the belly.
The head of the Arapaima is wide and flat, with a large mouth. Another distinctive feature of the Arapaima is its ability to breathe air at the water’s surface thanks to a specialized organ called the labyrinth organ. Scadeng et al., (2020) respiratory gas bladder is possibly the most surprising of all adaptations to living in the hypoxic waters of the Amazon basin, where dissolved oxygen can reach 0 ppm (0 mg/l) at night; and this unique adaptation allows the Arapaima to breathe atmospheric oxygen (Ramírez et al., 2018) and even venture into stagnant lakes and flooded forests.
On the other hand, paiches have ganoid scales that act as a flexible dermal armor and provide protection, mainly against attacks from piranhas, the main predators in the Amazon basin (Yang et al., 2014).
Despite its large size, the Arapaima is remarkably agile and swift in the water. Its body is streamlined and muscular, allowing it to navigate through dense vegetation in flooded areas and quickly catch its prey.
Currently, there is a genome of the paiche (Arapaima gigas), which provides a tool for differentiating between the different species of Arapaima.
Habitat and Distribution of the Arapaima
The Arapaima is native to the Amazon basin, specifically the rivers and floodplains of South America. It is predominantly found in Brazil, Peru, Colombia, Ecuador, Suriname, Venezuela, and Guyana. Within these regions, the Arapaima inhabits a variety of freshwater habitats, including rivers, lakes, and flooded forests.
The Arapaima is particularly well-adapted to the unique environments of the Amazon. It can tolerate a wide range of water conditions, including low oxygen levels and fluctuating water levels.
It is important to note that due to its potential for aquaculture and the ornamental industry, pirarucu has been introduced to countries such as China, Cuba, Mexico, the Philippines, Singapore, and Thailand (Ohs et al., 2021); as well as Bolivia, Indonesia, USA, Chile, and France.
Life Cycle and Reproduction of the Arapaima
Sexual Dimorphism
Paiches do not exhibit sexual dimorphism (differences between males and females) during the early years of life. This prevents fish farmers from selecting potential breeders to accelerate genetic improvement programs.
Many researchers have tried to establish methodologies to achieve sexing of the Arapaima in its early years of life; however, they have not been successful.
Chu et al., (2017) report that there are different methods of sexing breeders:
- Coloration pattern: This technique involves checking for a reddish-orange coloration stripe originating on the lateral side of the head, from the base of the mouth, passing through the operculum, and extending along the body of the fish.
- Sexing using ultrasonography: The use of ultrasound waves, a visualized using an ultrasound machine, is a successful method of sexing.
- Sexing using endoscopy: The fish undergoes minor surgery where a catheter—adapted with a camera—is inserted through a ventral incision into the peritoneal cavity to view the gonad.
- Biochemical methods: there are three biochemical methods for sexing the paiche: Determination of a relationship between blood levels of two sex steroids, 11-ketotestosterone and 17-β-estradiol, using kits; Use of an ELISA protocol to detect vitellogenin in the fish’s blood; and, Commercial kit for paiche sexing.
Recently, López et al., (2022) developed a molecular tool (PCR test) for sexing juvenile Arapaima, achieving 100% accuracy; while EMBRAPA (Brazil) provides the service of sexing pirarucu fingerlings.
Breeder Management
Currently, Arapaima breeders are kept in breeder ponds. Each breeder is “chipped” (intramuscular implantation of electromagnetic microchips, known in English as PIT tags) for individual fish identification.
Reproductive Behavior
The Arapaima follows a fascinating life cycle, which begins with the spawning season during the Amazon’s rainy season (December to March); however, in captivity conditions, it can reproduce throughout the year with systems simulating rains. Arapaima breeders normally range from 4 to 5 years of age (1.60 to 1.85 m).
As water levels rise, male Arapaimas, which acquire a red coloration near the jaw, build nests approximately 50 to 60 cm in diameter and 15 to 20 cm deep in shallow waters, using their powerful tails to clear vegetation and create depressions in the riverbed.
Females are attracted to the nests, and several females may deposit their eggs in a single nest, which the male fiercely guards. Previously, it was believed that the paiche was socially monogamous; however, research by Farias et al., (2015), based on Mendelian inheritance patterns, rejects this belief.
Hatching and Larval Rearing
Once the eggs are laid (2.5 to 3 mm in diameter), the male fertilizes them externally, and both parents take turns protecting the nest from predators. The eggs hatch after about 4 to 5 days, and the larvae must fend for themselves. The parental care period can extend for a period of 3 to 5 months; however, in aquaculture systems, extracting the shoal of paiche larvae from the breeder ponds is a widespread practice.
Santana et al., (2020) evaluated the effect of stocking densities on the performance and production cost of Arapaima larvae; they used larvae of 1.32 g and 5.90 cm and determined that the best density is 2000 larvae/m3.
As the larvae grow, they go through several developmental stages, gradually transitioning from a diet of tiny organisms to consuming small fish and invertebrates. The Arapaima grows rapidly during its early years, benefiting from the abundance of food in its habitat. However, as it reaches maturity, its growth rate significantly slows down.
Feeding Habits and Diet of the Arapaima
Feeding of the paiche in its natural environment
The Arapaima is a top predator in its ecosystem and feeds on a variety of prey depending on its size and availability. Its diet mainly consists of fish, although it can also consume crustaceans, insects, and even small mammals that venture too close to the water’s edge. In this regard, Villafan et al., (2020) highlight that the diet of paiches in natural environments such as the lagoons of the Madre de Dios and Beni rivers consists mainly of fish, plant material, and invertebrates.
Ohs et al., (2021) report that juvenile arapaima, less than a total length of 50 cm, have a varied diet including insects, fish, crustaceans, and mollusks; while paiches from 51 to 180 cm mainly feed on small fish; whereas Jacobi et al., (2020) revealed that young arapaima eat fish and invertebrates, but adult arapaima feed on fish from a wide range of species, mainly in lower and intermediate trophic positions, and also reports the first case of cannibalism for arapaima.
Regarding the morphology and histology of the pirarucu’s digestive tract, Rodrigues and Cargnin-Ferreira (2017) report that it is similar to that of other carnivorous teleosts and allows the species to ingest, store, and digest large food items.
Feeding of the pirarucu in fish farming
Arapaima larvae are fed with Artemia nauplii, zooplankton, or a combination of both. Subsequently, juveniles are trained to accept artificial feed. EMBRAPA published a manual with information on paiche feeding and nutrition; below, we provide somewhat specialized information.
dos Santos-Cipriano et al., (2015) conducted a digestibility test of four vegetable ingredients for feeding juvenile pirarucu (Arapaima gigas) and report that the best coefficients of apparent digestibility of crude protein were from corn (93.44%) and corn starch (90.94%) compared to rice bran (68.23%) and wheat bran (68.58%); while Chung et al., (2020) recommends dietary supplementation with 2.0 ml/kg of sweet basil essential oil Ocimum basilicum (EOOB) can increase the growth of pirarucu juveniles.
On the other hand, Pedrosa et al., (2019) evaluated different feeding strategies (use of feeders, manual feeding to satiety) in the rearing of paiche juveniles in recirculation systems for aquaculture, and concluded that feeding strategies can be used without compromising paiche rearing.
Luz et al., (2019) recommends including 1.17 g/kg of sodium butyrate in diets for A. gigas juveniles to improve growth parameters; as it favors feed conversion ratio, increases intestinal villus height, and promotes adaptation of enzymatic activity of amylase, lipase, and nonspecific alkaline protease. While da Costa Sousa et al., (2019) highlights the use of Enterococcus faecium for its probiotic effect on A. gigas juveniles and may recommend its use at a concentration of 1 × 108 CFU/g to modify intestinal microbiota, improve growth and hematological parameters, and reduce parasitic load; while do Couto et al., (2022) recommends the use of this bacterium to improve resistance to Aeromonas hydrophila.
Additionally, Dias et al., (2020) demonstrated that the inclusion of 6 and 8 g of brewer’s yeast Saccharomyces cerevisiae per kilogram in pirarucu diets increased final biomass, final length, body weight gain, daily weight gain, daily feed intake, specific growth rate, and decreased cholesterol levels.
Threats and Conservation Status of the Arapaima
Despite its impressive size and strength, the pirarucu faces numerous threats that jeopardize its survival. Overfishing, habitat destruction, and pollution are among the major threats to this majestic species. The large size and value of the Arapaima in commercial fishing have led to unsustainable fishing practices, resulting in significant population declines.
To address these threats and conserve the Arapaima, several measures have been implemented. These include fishing regulations, protected areas, and community management initiatives. Additionally, research and conservation organizations are working to raise awareness about the importance of preserving the Arapaima and its habitat, emphasizing the need for sustainable fishing practices and the preservation of critical spawning areas.
The pirarucu is listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) for protection since 1975.
Cultural Importance and Legends Surrounding the Arapaima
The Arapaima holds immense cultural significance for the indigenous peoples of the Amazon. For centuries, it has been a vital source of food, providing sustenance to communities living along the riverbanks. Its bones, scales, and other parts are also used in traditional medicine and craftsmanship.
The pirarucu is deeply rooted in the folklore and mythology of the Amazon. It is often associated with legends of powerful river spirits and mythical creatures that embody the strength and resilience of the Arapaima. These stories serve as a reminder of the deep connection between indigenous communities and the natural world they inhabit.
Arapaima Aquaculture
The pirarucu has excellent attributes for aquaculture, including its high growth rate, of around 10-15 kg in a period of nine months (Ohs et al., 2021) to one year, and an extraordinarily efficient feed conversion rate of FCR <0.7 (Du et al., 2019); in addition to quality and yield of meat, robustness and adaptability to handling and low concentrations of dissolved oxygen in water, spineless fillet, and skin and scales that can be used for leather and crafts production, etc. (Chu et al., 2017).
Table 01. Water quality parameters for Arapaima aquaculture.
| Parameter | Observed Range | Recommended |
|---|---|---|
| Dissolved Oxygen (mg/L) | 0.5 – 5.8 | >4.0 |
| CO2 (mg/L) | 2 – 22 | <20 |
| Nitrites (mg/L) | 0 | 0.05 – 15 |
| Total Ammonia (mg/L) | 0.2 – 3.0 | <0.05 |
| pH | 3.0 – 9.3 | 6.5 – 8.0 |
| Alkalinity (mg/L) | >20 | – |
| Temperature (°C) | 25 – 32.4 | 26 – 28 |
| Source: Ohs et al., (2021). | – | – |
Fish Farming
Currently, Arapaima aquaculture is conducted in semi-natural ponds, cages, and recirculating aquaculture systems. The characteristics of each system depend on factors such as stocking density and the location of the fish farm, among others. In our references section, you can find documents with more detailed information.
Size grading is a common management practice in aquaculture to minimize growth variability. However, Lima (2020) demonstrated that this practice does not improve overall pirarucu performance in captivity.
Arapaima is a tropical fish; however, experiments in temperate zones are being conducted. Lawson et al., (2015) determined that pirarucu cannot survive temperatures below 16°C in Florida (USA), while Ganoza et al., (2023) experimented with rearing under the temperate climate conditions of the central coast of Peru, where pond temperatures ranged between 23.0 and 24.6°C, achieving weight gains ranging from 3.4 to 20.9 g/d. They concluded that arapaima rearing could be viable in greenhouse conditions. However, Ohs et al., (2021) reported that temperatures below 24°C inhibit pirarucu growth, while temperatures above 32°C may increase arapaima susceptibility to diseases.
Utilization of Arapaima Byproducts
Arapaima Leather
Fish skin can be processed to produce leather for shoes, bags, wallets, belts, jackets, among other products. Cavali et al., (2022) evaluated the physical-mechanical resistance, histological, and morphological aspects of arapaima fibers for tanning with chromium oxide and vegetable tannin. They determined that pirarucu skin leathers tanned with vegetable tannin have lower resistance than leathers tanned with chromium salts in terms of tensile strength and higher resistance to tearing.
Moreover, Moreno et al., (2023) worked with extracts from quebracho (Schinopsis balansae) and mimosa (Acacia dealbata) to produce leather from pirarucu skin, achieving acceptable results.
Ohs et al., (2021) reported that small markets for belts, bags, and boots made from arapaima leather exist in the USA, citing Lucchese Bootmaker and Rocky Brands, Inc.
Arapaima Diseases
Diseases and parasites pose a significant challenge in pirarucu aquaculture (Ohs et al., 2021). Bacterial and parasitic diseases are the main headaches for fish farmers.
Bacterial Diseases
The bacterium Aeromonas hydrophila causes clinical signs such as dark skin, ulceration, hemorrhage, pale gills and liver, liver alterations, hyperemia, hepatic cord rupture, cell deformation, lipid degeneration, and necrosis (do Couto et al., 2022).
Parasites
Fish, particularly pirarucu, can be affected by a range of parasites. Murieta et al., (2020) described the main parasites affecting pirarucu during rearing in artificial systems, highlighting:
- Endoparasites: digenetic trematodes (Caballerotrema arapaimense, Caballerotrema brasiliense), cestodes (Schizochoerus liguloideus and Schizochoerus janicki), acanthocephalans (Polyacanthorhynchus macrorhynchus and Polyacanthorhynchus rhopalorhynchus), and nematodes (Camallanus tridentatus, Nilonema senticosum); and
- Ectoparasites: Monogeneans (Dawestrema cycloancistrioides, D. cycloancistrium, D. punctatum), branchiurans (Dolops discoidalis, Argulus sp.), Isopoda (Braga sp.).
Cruz et al., (2022) investigated the in vitro and in vivo efficacy of trichlorfon against Dawestrema cycloancistrium, as well as its physiological effects on arapaima, and determined that 150 mg/L of trichlorfon can be used in therapeutic baths to control and treat infestations by D. cycloancistrium. Malheiros et al., (2016) recommended the use of peppermint essential oil for bath treatments.
Moreover, Corral et al., (2018) recommended the use of Piper aduncum essential oil, which proved to be efficient and safe for controlling the Hysterothylacium sp. parasite, responsible for significant economic losses in the production of several fish species, including Arapaima gigas.
Regarding the Trichodina sp. parasite, Bentes et al., (2022) reported that a therapeutic bath with 20 mg L-1 of chloramine-T for 1 hour reduces trichodinid parasitism and does not affect the overall health of arapaima juveniles.
Conclusion
Arapaima is a true wonder of nature, embodying strength, resilience, and adaptability. Its impressive size, unique adaptations, and significant ecological role make it a species worth protecting and admiring. As we explore the fascinating world of Arapaima, we gain a deeper appreciation for the intricate web of life within the Amazon and the importance of preserving this delicate balance.
Through responsible conservation efforts and sustainable fishing and aquaculture practices, we can ensure that future generations have the privilege of encountering this majestic creature and marveling at its magnificence.
Currently, aquaculture practices are giving rise to an industry based on pirarucu; however, there are still some obstacles that must be overcome for this industry to be successful and sustainable.
References
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Cavali J, de Souza MLR, Silva de Oliveira Kanarski P, Coradini MF, Vieira Dantas Filho J (2022) Tanned leather of the paiche Arapaima gigas Schinz, 1822 (Arapaimidae) with extracts of vegetable origin to replace chromium salts. PLoS ONE 17(1): e0261781. https://doi.org/10.1371/journal.pone.0261781
Chung, S., LEMOS, C. H., Teixeira, D. V., Fortes-Silva, R., & Copatti, C. E. (2020). Essential oil from Ocimum basilicum improves growth performance and does not alter biochemical variables related to stress in pirarucu (Arapaima gigas). Anais da Academia Brasileira de Ciências, 92, e20181374.
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