Fish Care - Caring for Arowana

by Rupert Bridges, Tetra Information Centre

The common name ‘arowana' is used to refer to any one of seven species of fish, found in South America, Africa, Asia, and Australia. They are all members of an ancient order of fish called the ‘bony tongues' (suborder Osteoglossoidei ), referring to the bony plate on the floor of their mouths. This plate is covered in teeth, which are pressed against teeth in the roof of the mouth when capturing and processing food. One of the world's largest freshwater fish; Arapaima gigas , from South America, also belongs to this group. These fish can grow to 4.5m.

The most common species kept in aquariums around the world is the South American arowana ( Osteoglossum bicirrhosum ), whilst the most impressive is the Asian arowana, or Dragon fish ( Scleropages formosus ). Both these species have large barbels on their bottom lip, which are used to detect prey wriggling at the surface. According to Chinese mythology, the Dragon fish is said to bring good luck and business success to its owner, as well as ward off evil.

Another interesting fact about these fish, is that they brood their eggs and young in their mouths. This protects them against predators, allowing them to reach a reasonable size before they are released. Mouthbrooding is performed by male O.bicirrhosum , and female Dragon fish.

Aquaria for arowanas
Both commonly kept species of arowana are large, active fish, and therefore they require a big aquarium. O.bicirrhosum may grow to over a metre in length, whilst Dragon fish will normally reach around 90cm. Because of this, the minimum length of aquarium for adult specimens is 150cm.

Both species need good water quality, and so a powerful filter is essential. For O.bicirrhosum , a reasonable water current, coupled with good aeration, is beneficial. Dragon fish also need good filtration, but the amount of water movement created by the filter and airstone must not be too great.

Because they are active, and good jumpers ( O. bicirrhosum can leap up to 2m to catch terrestrial insects), the aquarium needs a tight-fitting cover. In addition, some floating plants to provide cover are appreciated, as these fish can be nervous. Because of this, the aquarium must be housed in a quiet area of the building. It should also be kept out of sunlight.

Keeping other fish with arowanas is generally not recommended, because of their nervous disposition. However, aquarists often put a large plecostomus in the aquarium (e.g. Glyptoperichthys gibbiceps ), to keep algae off the glass. These fish will remain on the base and sides of the tank, and are generally very peaceful. However, do keep a check on them, as very rarely they may develop a taste for the mucus on the sides of larger fish.

Maintenance
Because arowanas are large carnivores, they can produce a lot of waste. Therefore, it is advisable to change a portion of their water once every week or two. Change no more than 20% at a time, and ensure that new water is treated with Tetra AquaSafe to remove chlorine and heavy metals, and that it is the same temperature as the tank. The gravel should be kept clean, ideally by using a gravel siphon every few weeks.

Adding a supplement to the water, such as Tetra Arowana Vital, every four weeks, will improve health and colouration.

Buying arowana
It is relatively easy to get hold of O. bicirrhosum , although you should ensure that the specimen you purchase is settled (i.e. not freshly imported), and that it is feeding well. Dragon fish on the other hand are protected by C.I.T.E.S. (Appendix 1), which means that their sale from most parts of the world is banned. However, Singapore has special permission to sell them, as they are captive bred and therefore not a threat to wild populations.

Dragon fish are available in a number of different forms, each of which may command a different price. The simplest form is the ‘Green' Dragon fish, whilst the most revered are the ‘Red', ‘Axanthic', and ‘Albino' forms, with many other varieties in-between. Ensure that the fish you buy is from a reputable source, as some suppliers have been known to use unethical methods to improve colouration, such as blinding, exposure to sunlight, and the use of hormones. A reputable supplier will have used bloodline control, plus careful selection techniques, to ensure that the colouration is true, and that it will remain with the fish.

Introducing arowana to the aquarium
Once you have selected your arowana, it must be introduced to the aquarium properly, to ensure its survival. Float the bag on the surface for around 15 minutes, to get it used to the temperature. Then, slowly fill the bag up with aquarium water, over a period of 45 minutes. This will allow the fish to adjust to the water chemistry of the tank. Sudden shocks in temperature, hardness, and acidity, can cause sudden deaths, or at the very least, stress.

Do not feed your new fish for at least three days, to reduce energy use whilst it is still stressed. It is also a good idea to leave the aquarium lights off for a day or two (if you have any). Some Dragon fish breeders recommend that a temperature of 30°C should be maintained for the first week or so, to reduce the chances of bacterial infection. Alternatively, add a general anti-bacterial remedy to the aquarium, such as TetraMedica General Tonic. Reduce the temperature to 27°C for Dragon fish, and 25°C for O.bicirrhosum , after this period.

Feeding arowana
Both O.bicirrhosum and Dragon fish are carnivores. Juveniles tend to feed on smaller insects, whilst adults will eat fish. This diet must be replicated in captivity, to keep your arowana in top condition.

This can be done with fresh and live foods, plus good quality dry food. Because live and fresh food results in a lot of waste, lacks certain essential vitamins and minerals, and may carry disease, the bulk of the diet should be dry. Foods such as Tetra Arowana Sticks are based on large amounts of animal ingredients, such as shrimp and molluscs, in a highly digestible format. They also contain essential nutrients, and colour enhancers, to keep arowanas in top condition.

Juvenile arowana can be fed on dry foods 2-3 times a day, whereas adults only need 1-2 feeds. Occasional supplements with fresh foods, such as prawns, fish, live cockroaches etc, are acceptable, but ensure that they are well-washed. Any uneaten food should be removed immediately.