Silver arowana (Osteoglossum bicirrhosum)

Silver arowana (lat. Osteoglossum bicirrhosum) is a tropical freshwater fish of the Osteoglossidae family. Osteoglossidae genus appeared during the Jurassic period and hasn’t changed much during the last 150 million years. It’s a popular tank fish, which is often kept in zoos, public and amateur tanks around the world. In the East countries, it is a symbol of wealth and prosperity. Some fish species can rich dozen thousand dollars.

Habitat in the wild

Osteoglossidae family representatives can be encountered almost in all continents: South America, Africa, Australia, and South-East Azia. This is due to the fact that the fish is ancient. During the Jurassic period, Arowana predecessors inhabited supercontinent Gondwana that in after years divided into the continents which we know now.

The fish is native to South American river basins – such as the Amazon river, Rupununi, Orinoco, and Essequibo. The fish was introduced in North America several times arowana was caught in the USA, in ponds of different states. Fish inhabits backwaters and inshore zones of rivers and lakes with water temperature about +24…+30 °C. Each year during the overflow of the Amazon river, this fish swims into flooded bottomland forests. In the wild, it prefers wide river areas with a slow flow a bit aside from the flow center.

You can unerringly recognize surface waters dweller by the fish appearance. Its superior mouth, long straight back with far placed dorsal speak for it. The dorsal, together with the anal and tail fin, form a strong paddle that allows the fish to move abruptly.

When swimming upstream, it graciously curves the body from side to side, and at that, its sharp eyes don’t even for a second stop watching everything that is going on the water surface. Its two sensitive barbs on the mandible feel the tiniest water oscillations made by the insects that fall into the water. When detecting its prey, the fish abruptly jumps at it and opens its large jaws.

Silver arowanas are great jumpers, and locals call them «monkey fish.» If necessary, they jump up high from the water and catch insects and sometimes small birds flying by.

Description

The fish body may be up to 90 cm (35 in) long, more seldom – up to 120 cm (47 inches). Its weight is up to 6 kg (13 lb). On average, usually, it’s 4.6 kg (10 lb). Its tape-like body is rather flattened from sides, covered in very pale scales with some silvery glitter and golden tint.

The young fish body has yellow-orange stripes and some blueish glitter on it. The fish dorsal and anal fins are very long and narrow. They almost coalesce with its fluke. Together with the very wide and flattened tail-stem of the fish laterally, they form an unusual “paddle,” which gives arowana rather strong acceleration when the fish attacks its prey. It allows the fish to jump out from the water quite high to catch something. Once scared, arowana in a tank can jump out of it about 3 meters high.

Fish dorsal has about 42-50 rays and 49-58 rays in the anal one. Arowana’s body has 30-37 scales on its lateral line, and it has 84-92 spinal bones. The fish has a very wide upward-pointing mouth, and there are 2 fleshy barbels on the edge of its mandible. Most of the time, arowana slowly swims close to the water surface; at that, its barbels are pointed forward, and it looks like the fish is probing water by doing this.

Silver arowana can live in oxygen-deficient waters. Most of the time, it prefers staying in thickly planted waters which are quite often poor in oxygen content. That’s why it adapted and developed some additional ways of breathing.

The fish air-bladder has a wide net of blood vessels that ensures its functioning as a lung and dissolving oxygen in the blood. Some fish species have formed a special epibranchial organ allowing to capture atmospheric air.

Difficulties in keeping

This fish is definitely not for beginners. Even young arowana fish requires a spacious tank since it grows rather fast. A tank of 250 liters (66 gallons) is enough for young species.

However, rather quickly, the fish will require a bigger tank, about 800–1000 liters (265 gallons). Also, the fish needs very clean and fresh water. However, arowana, just like most freshwater fish, is rather tolerant to changes in water pH and hardness.

Besides, feeding arowana isn’t cheap.

Care and keeping in a tank

Scientific NameOsteoglossum bicirrhosum
FamilyOsteoglossidae
Common NamesSilver arowana, arowana fish, silver dragon fish
Ease of keepingMedium
Lifespan12 years and more
Tank size500 liters (132 gallons) and more
TemperamentPredatory
Tank typeCommunity of large fishes
DietOmnivorous
Temperature24 to 28 °C (75-82F)
pH6-8
Water hardness9–20 dGH
Sizeup to 120 cm (47 inches)

Lifespan

Provided with proper tank conditions, silver arowana can live up to 12 years.

Tank size

The most important condition to be observed is to keep this fish in a tank is the tank size. Recommended tank capacity must be over 500 liters (132 gallons). Minimal tank size is 160 cm long, 60 cm wide, and 50 cm high. This is a very long fish, and it should have the possibility to turn easily in the tank. An ideal tank size for arowana has to satisfy the following formula: the tank length has to be at least 3 times larger than the fish length, and the tank width should be not less than 1.2 of the fish size.

It’s acceptable to keep young arowana in smaller tanks temporarily. However, later the fish must be taken into a properly sized tank to avoid its body deformation and ensure its maximum lifespan and body length. The tank has to be securely closed with some glass cover to prevent the fish from jumping out of it.

The fish spends time mainly near the water surface, and the tank depth isn’t crucial for it. However, a transparent cover for the tank is a must since arowana may instinctively try to catch any insect and jump from the tank.

Water parameters

Wild silver arowana prefers soft water with pH values from 6.0 up to 8.0, but in a tank, it is not demanding to the water chemical content. It easily adapts to tank water with a wide range of hardness and acidity. Tank water temperature should be from 24 to 28 °C (75-82F); ideally, it should be close to 26 °C (78°F).

Tank setup: decorations and plants

Actually, this fish doesn’t care much about the tank interior since it spends most of its time in the upper water layer. The tank is usually decorated as its natural biotope. Sand or small pebbles are used as a bottom substrate. Stones and snags are used as decorations. As for the live tank plants, Vallisnéria gigantea is a good choice, but you should surround it with stones so the fish won’t dig it out. The tank lighting shouldn’t be bright. Ideally, you need lighting fixtures that will switch on gradually not to scare the fish.

Filtration

The fish requires strong water filtration, 25-30% water weekly renew, and tank cleaning to keep the proper water characteristics. Silver arowana is tolerant to excessive nitrate content in the tank water, but even a small concentration of ammonia and nitrites is dangerous for it, therefore a canister filter and regular water renews are a must. This large fish produces a lot of waste, and they should be removed from the system.

Feeding

Fish hunts mainly close to the water surface. It is an omnivorous one, but it feeds mainly on fish. However, it eagerly catches large insects (mostly bugs), spiders, crabs, snails, frogs, and other small inhabitants, including terrain and tree-dwelling ones, which sit on the branches and leaves above the water, and arowana jumps out of the water to get them.

It is said that even snakes and birds were found in arowanas stomachs as well as some plant remnants, which speaks for the fact that the fish really is an omnivorous one.

In the wild, arowanas eat food with a huge amount of bulk substance – such as bird feathers, insects, chitin, etc. It means that you should feed the fish in a tank correspondingly to all those mentioned above. The fish diet may include large insects, shrimps, fish (not more than twice a week), large species may be fed with small animals, for example, mice.

You may also use some special food made for arowana. You mustn’t feed the fish with food that drowns all the time since it may cause the fish’s eye focus shifting (cross-eye). In the wild, it spends most of the time scanning the water surface for prey, while in the tank, it will learn to look down if it will be fed with the food that falls on the tank bottom. Some time later, one of its eyes will constantly look down, so-called drop eye.

A large amount of fat food also may cause the same disease because too much fat leads to relaxation of skin structure under the diseased eye. In the wild eyes of healthy fish are directed vertically, not downwards.

Frogs are the favorite food of many arowana species. They may get used to it that much that they’ll stop eating any other food. You can buy frogs in a pet shop or on the market.

Feeding with live small fishes will let you observe the process of arowana hunting, so it’s not only just some nutritive food for the fish. Such fish should be selected according to the size, so arowana would easily swallow them. It shouldn’t be any gorefish, and it shouldn’t have any sharp poisonous pins. Another rule – this must be a tank fish without any infectious diseases.

Tank mates

When buying arowana to keep it in your tank, keep in mind that this is a predator fish. However, it does well with other tank mates if they are 3 times larger than it is.

Silver arowana can be kept together with black ghost knife fish, blood parrot, oscar fish, flowerhorn, large clown loach, black pacu, giant gourami, plecostomus). However, any smaller fishes, for example, african cichlids and goldfishes, will be treated as food. If you wanted to keep arowana and angelfishes, I wouldn’t opt for this. Arowana won’t eat large angelfishes, especially altum angelfish, but it may eat smaller ones.

There should be no more than one adult arowana in a tank since this fish tends to be aggressive to the species of its kind. Wild arowanas demonstrate strongly marked hierarchy when a dominating species selects and occupies a specific territory and attacks any relative that tries to come close. For this reason, adult arowanas are mostly kept alone to avoid possible conflicts between the species.

Gender differences: male vs female

Gender dimorphism is rather poorly pronounced here. The males have longer anal and dorsal fins, and their bodies are more gracious with a larger head. They demonstrate quite aggressive behavior. It is easier to see between the male and the female during the spawning period. The latter has a rounded abdomen with eggs and looks fatter than the male.

Breeding

The fish spawning period starts at the beginning of flood. The female fish lays a small number of eggs, which the male fish carries in his mouth. According to the observations in captivity, male fish incubates the eggs for 40 days. The eggs are very large, red-orange, drop-shaped with a high amount of nutrient substances.

Arowana juveniles hatch being 3 cm large. After that, they continue staying in one of their parents’ mouths, and they swim out from time to time. Their yolk sac continues to be the source of food for juveniles (they are 6-7 cm long). Young fish leaves its parents’ mouth 5 weeks later since the day it hatched. After the juvenile’s yolk sac comes to an end, they start eating the food you give them.

The juveniles must be separated from the adult species as soon as possible. Usually, to do this, they force the breeder to open its mouth or wait till the juveniles leave it themselves. The approach used depends on the breeders’ behavior. If they take care of their juveniles, the natural way is more preferable — otherwise, the first option is better. Both approaches will not only ensure the safety of the juveniles but also will shorten the time left to the next spawning.

Nowadays, there are only three proven cases of successful silver arovana breeding in captivity. Therefore, the fish is bred in fish farms of South-East Asia using hormones.