Arapaima gigas, one of the largest freshwater fishes in the world, inhabits the basins of the Amazon and the Essequibo Rivers and can reach a length of 10 feet (3 m) and a weight of 440 pounds (200 kg). Because of the delicious taste of its meat, it has traditionally been one of the most important food fishes of Amazonia. Unfortunately, stocks have declined greatly.Most Arapaimas inhabit lakes, but they can also be found in rivers and, during the low-water season between September and January, in the interconnecting channels. During this time, the animals spawn. They migrate through the channels from one lake to another, looking for suitable spawning grounds. They usually prefer shallow seasonal waters, known as resaca, that often completely disappear in the dry season. Rarely, the fish remain in permanent waters and channels known as parana, which cross the varzea, the periodically flooded areas that connect the rivers.
In general, the spawning areas are shallow waterswith low currents. The shallow depth allows people to catch the fish, but also allows the fish to quickly reach the surface to breathe. In this way, they reduce the risk that their offspring will be eaten by other fishes when they go up for air. Furthermore, the fry can easily get to the surface during the critical phase in which they switch to using their swim bladders for breathing air.
A round, flat nest is dug into the sand at a depth of just 3-5 feet (1-1.5 m). Depending on the size of the parents, a pair digs a nest 8-28 inches (20-70 cm) wide and up to 4.7 inches (12 cm) deep. The animals take three to five days to build the nest. They also clear an area of approximately 6.5 feet (2 m) around the nest, removing anything that predators could hide in. By removing all the oxygen consuming organic litter, they probably also improve the oxygen supply to the fry. The nests are usually far away from floating vegetation. Even at high density, there are only one or two nests per 0.6 mile (1 km) of shoreline.
The pair spawns immediately after completing the nest. In the depression of the nest, the eggs are protected from currents and predators. Five days after spawning, the young, perhaps numbering 1,000 or more, hatch. Now the female disappears and sometimes even spawns with another male in the same season.
The male protects the fry by staying close, not moving farther away than 39 inches (1 m). For three months, he leads the fry through the flooded forests, where they feed on insects and fish larvae. In this habitat, the low density of predators and the abundance of food ensure that a large number of young fish grow up. The areas of floating islands are especially ideal habitat for the growing fry.
They grow up fast: after three months they are already 12-20 inches (30-50 cm) long.
When the water begins to recede from the flooded forest, the male leaves the offspring, and they spread through the channels in search of permanent waters, such as lakes. The juveniles avoid unsuitable habitats. They change constantly between chavascal, or igapo, rest-inga (wooded sandbanks, named high or low, depending on the height and age of the vegetation), parana, cano (temporary connections between lakes and other bodies of water), and the river itself.Migration of the juveniles
During the high-water season on the upper Amazon— from January to April—one can find Arapaimas in the flooded forests of the chavascal or igapo (in Brazil) and along the high and low restinga. Because they are able to breathe air, they can survive the low oxygen content of these habitats. With their elongated bodies, they are also well adapted to these shallow waters. The fish prefer water under 10 feet (3 m) deep and low currents so they can conserve energy.
At the age of one year, Arapaimas feed mainly on fishes and therefore forage in freshly flooded habitats, wherethere are many small fishes—especially the well-known aquarium catfishes of the families Callichthyidae, Lori-cariidae, Pimelodidae, and Heptapteridae. The species of the first two families can also survive in this oxygen-poor habitat because they are equipped with bowel breathing.
During the low-water season, Arapaimas are mainly found in lakes. When the water level drops, the populations of their prey fishes become denser. Many of these fishes perish due to high temperatures of 81-88°F (27-31°C), low oxygen concentrations, and poor water quality. For the Arapaimas, this is a feast. Here they meet their partners, perform courtship, and then, toward theend of the dry season, migrate to the places where they will spawn.
Due to the decline of their stocks, the Brazilian government has regulated the catch of the Arapaimas, or Pirarucus (the Indian word pira stands for fish and urugu is the Indian name for Achiote, Bixa orelliana, whose seeds supply the red pigment for body painting). Brazil introduced a minimum size limit for the fish caught, prohibited fishing during the spawning season, and even imposed a fishing moratorium for the state of Amazonas. However, because of widespread illegal fishing and the lack of effective controls over the vast territory, these measures are far from adequate.
The Arapaima is mainly threatened by spear fishing; since they must come to the surface to breathe every 15 minutes, they are easily killed by experienced fishermen. During the spawning season, the animals are particularly vulnerable. They create their nests in shallow water and are easy to spot, despite the cloudiness of the water during this time. The males are also at risk during brood care.
Arapaima gigas has now completely disappeared from the waters in the vicinity of cities and settlements. Overexploited in the rest of the Amazon basin, the species is considered endangered to critically endangered. The only somewhat successful measures are those that protect the habitats of the Arapaima and restrict the fishing season. Concerned observers are calling for new protections for their spawning areas as well as the flooded forest areas when the fish are most vulnerable.