Osteoglossum bicirrhosum

Order: Osteoglossiformes
Family: Osteoglossidae
Genus: Osteoglossum
Species: Osteoglossum bicirrhosum, Cuvier, 1829

Osteoglossum bicirrhosum, is a fish in the family Osteoglossidae and is commonly known as "Silver Arowana". It is the largest Arowana species which can grow to a maximum size of 130 cm and have a weight of more than 10 kg in nature.

Its common body shape is long and snake - like, but flattened to the sides. The dorsal- and anal fin extend over the back half of the arowanas body. The other fins are comparable small and especially the caudal fin appears smaller the older the fish gets. This species has a deeply cut mouth that faces upwards to the surface, allowing them to open it at a wide angle. They also have two short barbels that point upwards and feel, as it were, the water surface from below when the fish swims.
The overall coloration is with adults silver-white, which can also appear sometimes more beige or blueish. Youngsters are more colorful and show more blue in the body scales and more red in the fins, than adults.

Arowanas are fast growers and reach their sexual maturity in 3,5 years, with a size of around 50 - 60 cm.

During the day, this fish constantly patrols the surface of the water in search for food. Only while sleeping or when threatened this fish reaches for deeper water to stay still and hide. This hiding behavior can be seen more often in younger individuals, who are easier prey for larger predators. Osteoglossum bicirrhosum is a powerful fish, which can jump high out of the water, to reach prey, sitting on branches over the water surface. Because of this ability, Silver Arowanas are sometimes called "Monkey Fish". Other than that, this species is also known under the synonyms "Aruanã "or "Arahuana".

This species has a wide distribution in Brazil, Guyana and French Guiana. There you can find them in the tributaries of the Rio Amazonas, the Rupununi River and the Oyapock.

Osteoglossum bicirrhosum prefers slow streaming, flooded side areas of the main rivers. There it swims low under the water surface, looking for food in the branches over the water.

The water is in all of its habitats over 24 °C warm and can reach up to 30 °C. The pH and hardness of the water differs from river to river but is mostly slightly acidic and soft.

This fish is mainly a carnivore but from time to time it also takes plant matter, like fruits, nuts and leafs, that fell into the water.

This fish is one of the top predators in its habitat, since its one of the longest fish with a huge mouth. Additional to prey that it catches in the water (fish, frogs, water insects, worms, etc.) it also hunts prey on and above the water surface. Fallen insects, birds, swimming rodents and even bats can be caught by this powerful fish. You can regularly observe that this fish jumps high out of the water to reach prey that sits on branches above the water. With snake like wiggles, it can leap up to 1,5 - 2 meters above the water surface.

In captivity you can offer this fish a wide range of food. When this fish is added fresh to the aquarium, it can take several days before it starts to eat. When small, it is possible to feed Arowanas with smaller, floating food, like mosquito larvae, flakes or little pellets. Also insects, like little, locusts, crickets, meal worms etc. are a protein rich food, which is taken mostly really good.
The bigger the Arowana gets, the bigger the food has to be chosen. It is possible to feed big floating carnivore pellets (like Hikari Jumbo Carnisticks), mussels, shrimps and fish filet. Feeding Arowanas with warm-blooded meat such as beef heart is not necessary. Also, feeding live vertebrates like feeder fish, frogs, rats and mice and chicks is not necessary as arowanas eat dead and processed food without any problem. In addition, it is against animal protection laws!

This fish is one of the biggest tropical fish commonly kept, and sadly also mostly in too small tanks. Silver arowanas can grow to 100-120 cm in captivity and are active swimmers. For adult specimens, tanks big enough can mostly only be seen in public aquariums or zoos. Around 5.000 - 10.000 liters should be available for them. Nonetheless is the keeping of younger individuals in most cases not so a problem. For Arowanas from 15 - 50 cm a tank with a length of 2 - 3,5 meter is good, but not a final solution. The height doesn't matter as much as the length, but shouldn't be chosen under 50 cm.

Arowanas can be skittish and startle easily. Their first reaction is to flee, resulting in jumping or swimming quickly in the opposite direction of the danger. Therefore, much decoration in the aquarium can be counterproductive, as these fish have a tendency to hurt themselves if they crash into it. So in general it is better to avoid sharp and pointy rocks or driftwood when setting up an Arowana tank. The substrate really doesn't matter, since O. bicirrhosum spends most of his life under the water surface.

The next important thing is a strong lid. Since Arowanas are excellent jumpers, they maneuver through every small hole they spot and fit through. A well-closed aquarium prevents the Arowana from jumping- and drying out on the floor.
The bigger the animal gets, the heavier the lid has to be, 10 kg of fish can make a lot of damage! Best is to use plastic/PVC lids, because they don't break easy and prevent the Arowana from smashing its head. Glass lids can break and cut the Arowana, which results in deadly blood loss.

Another important point is the filter of the aquarium. Because this species produces a lot of excretions due to the high demand for food, a good filter must be present.
Weekly water changes of at least 50% are mandatory. The aquarium water should be about 25 - 29°C. Take care that the heater is outside of the reach of the fish, because also that can be damaged by the Arowana, when it gets spooked. Try to stay neutral to slightly acidic with the pH and don't add to much minerals to the water.
Arowanas are day active and orientate on light. So it makes sense to have a light on for 10 - 12 hours a day. Also here the light shouldn't be under the lid, since the Arowana could jump into it.

It is possible to keep Arowanas alone, in groups (if the space allows it) or with other fish. It should only be taken care that the tank mates don't fall into his food spectrum. So a lot of bigger cichlids, tetras and plecos are a good choice for companions. Especially big plecos inhabit a total different zone in the tank, which gives those two fish the possibility to go out of each's ways.

To sex O. bicirrhosum is in most cases not so difficult, even though it gets easier, the bigger the fish gets.

Males tend to stay a bit thinner and less voluminous than females. Sub- to adult males also develop a longer lower jaw, which overlaps the upper jaw. This and a bigger throat pouch, are necessary for mouth brooding, which is the males job. It is also said that younger males are more colorful than females.

Males are generally more aggressive and faster eaters. When you keep them in groups with both sexes, they are the first ones at the food.
Females are a bit more shy and startle more easily.

Arowanas are mouth brooders and usually only breed once a year. Courtship starts with male and female swimming in circles and building a nest (sand ditch) on the ground. This can go on for several days.

When the female is ready, she lays 30 - 50 orange eggs on the floor. At the same time the male fertilizes the clutch while shaking his head quickly.

The male then swims sideways with his head towards the eggs and carefully collects them with his mouth. He then keeps them in his mouth/gill sac where he will protect and incubate the eggs for the next 50-60 days. After about these two months the fully developed babies will leave the protective mouth, they are then 6 - 10 cm tall.

In captivity Silver Arowanas are mostly bred in outside ponds, since they have a high demand on space. They often take the babies out of the father's mouth just before he releases the youngsters into the water.