Silver arowana

The silver arowana (Osteoglossum bicirrhosum) is a South American freshwater bony fish of the family Osteoglossidae. Silver arowanas are sometimes kept in aquariums, but they are predatory and require a very large tank.

The generic name Osteoglossum means "bone-tongued" and the specific name bicirrhosum means "two barbels" (from the Greek language).

Range and habitat
This South American species is native to the Amazon, Essequibo and Oyapock basins. It is absent from the Rio Negro basin, except the Branco River, which is inhabited by both silver and black arowanas.

The silver arowana occurs in both black- and whitewater habitats, including flooded forests.

Description
This fish has relatively large scales, a long body, and a tapered tail, with the dorsal and anal fins extending all the way to the small caudal fin, with which they are nearly fused. Its maximum total length is typically considered to be 0.9 m, but there are reports of individuals up to 1.2 m. Unlike the black arowana, the silver arowana has the same coloring throughout its lifespan. Adults of the two species are very similar, but can be separated by meristics.

Arowanas are sometimes called 'dragon fish' by aquarists because their shiny, armor-like scales and double barbels are reminiscent of descriptions of dragons in East Asian folklore.

Behavior
The species is also called 'water monkey' because of its ability to jump out of the water and capture its prey. It usually swims near the water surface waiting for potential prey. Although specimens have been found with the remains of birds, bats, mice, and snakes in their stomachs, its main diet consists of snails, crustaceans (such as crabs), insects (such as beetles), spiders, smaller fish, and other animals that float on the water surface, for which purpose its drawbridge-like mouth is adapted.

Conservation status
The silver arowana is not currently listed on any CITES appendix and is listed as Least Concern on the IUCN Red List. It is one of the most popular ornamental fish from South America, however, and therefore its conservation status merits attention. Other threats include droughts and deforestation, siltation and drainage of land for human use.

As reported by Environment News Service in August 2005, shared use of the silver arowana population was a cause for a dispute between Brazilian and Colombian authorities. Juvenile silver arowanas are caught in Colombia for sale as aquarium fish, while the people of Brazilian Amazonia catch adult fish for food. A sharp drop in the number of arowanas had caused Brazilian authorities to prohibit fishing of them between September 1 and November 15; the Colombians would prohibit capturing them between November 1 and March 15.

The silver arowana is often kept as a pet by experienced aquarists, being considered an accessible substitute for the Asian arowana, which is listed on CITES Appendix I and is therefore difficult and expensive to obtain legally. <!-- how-to, uncited

Aquaria
To keep one of these large fish, a properly sized aquarium is important. The minimum recommendable tank size for one adult silver arowana is 300 gallons (8'X3'). At no time should an arowana be kept in a tank that is narrower and shorter than the length of the fish. A young specimen can be kept in a smaller tank, but as it grows a larger tank will be necessary to prevent deformities and to ensure the maximum length and life span of the animal.

Any aquarium housing an arowana should be tightly covered because of these fish's jumping behavior. Also will jump out the water and attack the hands of people that are above the tank.

Water conditions
Silver arowana prefer soft water with a pH level between 6.0 and neutral. Strong filtration is necessary for these large carnivores. Commercially available blackwater additives can help simulate the silver arowana's natural habitat, although they can adapt to most water supplies and thrive. A 25-30% water change, siphoning waste and other detritus, is necessary 1-2 times every week to maintain excellent water conditions. The water temperature should range from 24°C (75°F) to 28°C (82°F), with the ideal about 26°C (79°F).

Feeding
Silver arowana may be offered meaty foods such as insects, shrimp, fish, frogs, pellet foods, etc., though it is best to feed arowana a brand of floating pellet food that has been specifically processed for fish of this type. There are several types of food on the market from some of the larger name brand makers of fish products that are made with this species in mind. Feeding arowana in this manner will help avoid dropeye, a condition in which one of the eyes are turned downward. In the wild, the arowana spends most of its life scanning the water surface for prey, but it will learn in an aquarium environment to look downwards for food that sinks to the bottom of its tank. Over time, one eye will permanently droop downwards. However some arowana fed exclusively on floating food pellets have also developed sudden dropeye after violently colliding with the tank. Another condition that can develop is "cloudy eye"; one or both of the eyes become scratched when the arowana turns itself sideways to collect food from the bottom, causing them to cloud over. The cloudy eye condition is treatable, while the drop eye condition is not. Keeping an arowana almost exclusively on a pellet diet will not only provide the fish with a well balanced meal, it is more cost effective and will generally prevent health issues. Many aquarists recommend against live feeder fish because these are often raised in poor conditions and are capable of transmitting diseases to predatory fish. Other risks include injury to the arowana either while attempting to catch the feeder fish, or while swallowing. Mealworm exoskeletons are sometimes difficult for young arowana to digest, so they are best avoided.

Tankmates
Silver arowana can be kept with other freshwater fish as long as they are too large to fit in the arowana's mouth and can tolerate the arowanas active-swimming lifestyle. Many people like having more than one arowana in the tank; in this case, hobbyists recommend keeping at least five to six in the tank at a time because silver arowana are not aggressive towards each other but must be raised together and need to be the same size. -->