Арапайма: Биология, Распространение и Экологическое Значение

Species of fish

Arapaima gigas, also known as pirarucu or simply arapaima,

The species is among the largest known freshwater fish, commonly measuring and reportedly exceptionally reaching lengths of up to Adults may weigh up to A. gigas has a streamlined body with dorsal and anal fins set well back towards the tail. While the body is mainly gray to gray green, its Brazilian local name pirarucu derives from an indigenous word for "red fish", thought to refer to either the red flecks on the scales towards the tail, or the reddish orange color of its meat. The fish have "flexible, armor like scales" made up of "a hard, mineralized outer layer" and "a tough but flexible inner layer" that help protect it from attacks by piranhas.

A. gigas is native to freshwater in the basin of the Amazon River; it is known to occur in Bolivia, Brazil, Guyana, and Peru. and presumably introduced from Peru being washed out of a Peruvian fish farm by a flood. The species has been introduced to parts of East Asia, both for fishing purposes and accidentally. A 13 million year old fossil of arapaima (or very similar species) has been found in Colombia, in the Villavieja Formation, which dates from the Miocene epoch.

Morphology changes occur as A. gigas undergoes the transition from water breather to air breather 8–9 days after hatch. During the transition to air breathing, the structure of the gills changes, making them better adapted for ion absorption, but less able to undergo gas diffusion. Once developmental changes in the gills take place, the lamella is less recognizable. The adult gills are made up of smooth, column shaped filaments, instead. The kidneys have an important role in nitrogenous waste excretion in this species and are enlarged in adult fish. The secretion is made of 400 substances and consist of hormones, proteins, peptides and likely pheromones.

A. gigas requires breathing surface air to supplement the oxygen it derives from the use of its gills, and as such, is dependent on surfacing every 5–15 minutes to loudly gulp air at the surface. As in other species in the genus, a modified swim bladder that contains lung like tissue is used for this purpose. The species primarily feeds on fish, although juveniles prefer insects and fish larvae until fully grown. They also consume birds, mammals, fruits, and seeds on the water surface. Spawning occurs in lakes and river channels during the time of low water levels (August to March). After the young hatch from eggs laid in a nest constructed by both parents, the male remains to protect them for a period of about three months. The young reach sexual maturity at an age of four to five years; average lifespan in captivity is 15–20 years. For Bolivia, the paiche as an invasive species is considered a threat to local native species according to reports. Various reports show a correlation between the spreading of paiche and the decline in numbers of native fish species in parts of the Bolivian Amazon. Effects on local fish species populations and on fishing behaviors vary strongly by region.