Osteoglossiformes - Aruana and Arapaima
Osteoglossiformes are an extremely ancient order of prehistoric freshwater fishes. The arapaima, paiche or pirarucú, as it is known in Brazil, is the largest, scaled, wholly freshwater fish in the world. Fish of 4 meters (over 12 feet) and up to 300 kg (660 lbs) have been recorded. At first glance, pirarucú look like an Amazon version of a tarpon, with a similar profile save for their flattened head and strange, club-shaped tail. The pirarucú's flesh is much sought after throughout the Amazon and for this reason, large specimens are becoming very rare.
Although not usually pursued as a sport fish in the Amazon basin, pirarucú can be taken on conventional tackle with a little patience and a lot of persistence. They have been caught using a variety of large (7-inch or so) jerk baits (14-18 size Rapalas, big Bombers and Red-fins), although a large live baitfish (on a 14/0 circle hook) dropped under a big float is probably the best bet in areas where anglers are common.
Arapaima will, on rare occasions take a streamer fished in the deep lagoons it prefers to haunt. They are normally a very wary fish and must be approached with extreme caution. However, when guarding a spawning site, they have the unsettling habit of surfacing close to your boat like a giant scaled submarine, on occasion even leaping entirely clear of the water. Considering their size, and their brilliant array of gold, red and purple spawning colors, this is an impressive performance. Pirarucú are obligatory air-breathers with both gills, which they use to exchange gases, and a modified air bladder that acts like a lung, which they use to gulp in air, supplying supplementary oxygen. Stout tackle is a must for these giants - For the determined fly fisherman, an 11 or 12-weight rod, 400-grain sink-tip line, heavy leaders and large streamers tied on 7/0 heavy saltwater hooks are standard equipment.
Though pirarucú are sometimes found in 'fishable' numbers, it is important to note that a great deal of time, patience and probably plain luck must be devoted to the fish if one is to catch one on a fly rod. It is not an everyday occurrence in peacock bass waters.
The aruanã (Osteoglossum bicirrhosum) is a close relative of the pirarucú. They are a schooling fish that can reach a maximum weight of about 20-pounds. They are often plentiful in certain peacock bass waters and can make an interesting accompaniment to a peacock trip. Aruanã are extremely surface-oriented and can often be sight-fished as they cruise about just below the surface in search of prey. They take the same lures used for smaller peacocks (and especially love Heddon Zara spooks). They are a delight for fly fishermen. A 7-8-weight fly rod, floating line and a variety of medium-sized poppers and sliders (2/0) make for some exciting fishing. When hooked, aruanã repeatedly jump like a baby tarpon.
Pirarucu - Arapaima gigas
Why Breathe Air?
Amazon aquatic environments are influenced dramatically by the region's unusual characteristics. Seasonal rains can raise and lower water levels by as much as 40 feet. Daily variations in temperature and photosynthesis (plant respiration) can cause wildly varying levels of dissolved oxygen in some Amazon waters. As a result, many Amazon fishes are routinely subjected to periods when their waters contain extremely low levels of oxygen (hypoxia or anoxia).
In order to survive these deadly conditions, many species have evolved unique respiratory strategies. Some absorb oxygen through their skin, others take advantage of multiple versions of oxygen-carrying hemoglobin in their bloodstream. Many species simply migrate to avoid the difficult times. The arapaima, however, has literally risen above it all.
These lumbering Amazon giants simply rise to the surface and gulp air. Their modified swim bladders act as lungs, dispersing oxygen into the bloodstream. Their gills return the waste CO2 gases to the water. It's a neat system that allows arapaima to swim blithely along in conditions that would rapidly suffocate other fishes. Millions of years of evolutionary adaptation enabled them to prosper and proliferate throughout the Amazon. Nature's work however, is often quickly undone by man.
This once plentiful species suffers the misfortune of being particularly tasty. The same air-breathing mechanism that allows them to survive the worst possible natural conditions proves to be their undoing when it comes to mankind. They are obligatory air-breathers -- and they must come to the surface in order to breathe. They would drown, just like us, if they couldn't periodically gulp air. This makes them an easy target for patient, harpoon wielding hunters who bring their flesh to market. Only recently have measures been taken to protect this magnificent Amazon giant.
Aruanã - Osteoglossum bicirrhosum
The natives call this odd-looking silver creature "macaco da agua", "water monkey" because of its ability to leap high out of the water to snag prey. In addition to small fish, aruanã eat insects, small birds, bats and reptiles, which they will often snatch from overhanging branches.
Their large, light-reflecting, opalescent scales and their fluid swimming movements make them underwater billboards for the sight fishing angler. They take a bait by opening their cargo-door mouth, inhaling it and then closing the gate. Although not a particularly powerful fish, they are highly prized as a gamefish by many.
The aruanã is also a very popular aquarium fish. They give observers a peek into a prehistoric world.