Tankmates for your arowana

Before attempting to keep any tankmates with your arowana, the most important factor to consider is whether your arowana will be better off with the tankmate. Every arowana has a different temperament, and therefore will react differently to the tankmate. If the tankmate spooks the arowana causing it not to eat, then it is obviously not advisable to continue having the two in the same tank. The material here gives the hobbyist a better feel of what can be suitable based on the experience of members.
Some of the observations are given in this thread by members. Members may continue to add their comments to the thread and I shall update this material on a best effort basis.

The list of tankmates may seem long for someone new in the hobby.
Favourite tankmates that work with most arowanas are Birchirs, Silver Dollars, Red Hooks, Emperor Hooks, Tin Foil Barbs, FF (Semaprochilodus taeniurus). Red Tail Cat is a worthy arowana companion as according to one hobbyists, he noted that the arowana seems to want to eat more as it is afraid the RTC would outgrow it. The more adventurous keep Tigers (Datnoids), Dorados, etc with their arowanas

1. What are the tankmates that can be kept with arowanas?
Generally, any fish that is bigger than the aro's mouth plus not shiny/silver should survive arowana tanking.
Avoid aggressive/fin biter fish eg umbees.
Fast aggressive food chasers may not be good for juvenile aros eg 6 banded fasciatus( out-chased & out-ate my young aros )
The rate of growth of the tankmates can change the fine balance of power in the tank. If the tankmate outgrows the aro, they can pose a danger to the aro and should be removed.

2. What are the advantages of keeping tankmates with aros?
Provide companionship & competition for food : increases aro interest in feeding.
Aros are most times top level swimmers, having mid- & lower- level swimmers makes for better aesthetics
Aggression dispersal - instead of targeting one tankmate, by introducing non aro as tankmates, the aggression can be dispersed over more numbers, hence the risks of continuous attack against another aro is reduced.
Some tankmates can help to clean the tank bottom by clearing leftover food
Other tankmates can be effective tank and glass cleaners

Group 1 : Bottom Feeders
1.1 Plecos (Loricariidae)
High bioload, spikes may harm aro's eyes, bottom feeders
Panaques, especially royals can be very efficient tank cleaners but they must be given drift wood and algae wafers. They cannot be expected to clear leftovers as they are herbivorous. But they certainly can clean the tank of algae, and this is done in the night time when the owner is asleep, it is at this time when the Royals are most active.
Pseudacanthicus (eg L14, L24, L25, L600, etc) are carnivorous feeders, however, they do not consume a high volume of food and are therefore not efficient in clearing leftovers.
Plecos can be good tankmates provided the specimens chosen are not too big to threaten the aros with their spikes. Plecos are also slow growers.
A consideration for putting in plecos is the beauty it lends to the tank without additional stress on the arowana.
1.2 Catfish (Siluriformes)
RTC (Phractocephalus hemioliopterus) is a very efficient cleaner as they consume large amounts of food and are not choosy. However, these grow very fast and is likely to be able to outgrow the aro, and therefore pose a threat to the aro. Keeping RTC that are smaller than an aro is ideal as the aro is motivated to eat. They also look comical and can be very entertaining.

1.3 Birchirs (Polypterus)
Endies, and other birchirs are very efficient in cleaning leftover food as they are big eaters. Birchirs are not fussy with food, therefore they can be easily maintained. However, large endies may threaten small aros.

1.3 Tigrinus, Jurus
They are carnivorous, and feed on live food, but can also be trained to take MP and pellets. Maintaining Tigrinus in an aro tank is more challenging because of their food requirements. But they are very beautiful and pleasing to the eyes due to their striking blue and striped body.

1.4 Rays
Contributes a very high bioload to the tank, they require a carnivore diet. In the event that the tank may need to be treated (if the aro requires medication), the ray's sensitivity to several medication needs to be taken into account. Managing a tank with ray and aro combined over the long term could be a challenge.

1.5 Clown Loach
Very pleasant to the eyes, and can be effective tank cleaners as they consume MP and pellets, they are omnivores. However, they tend to hide and therefore may suffer if there are dead spaces in the tank where there is little or no movement of water.

1.6 Spiney Eels

Some common species that are suitable as tankmates will be peacock (max 1ft), fire (max 3ft) n tyre track (max 3ft).
They can be easily trained to take MP and will feed on MP greedily. Not a very aggressive fish. need to have hiding area. Prefer to hide during the day.

Group 2: Mid Water/Surface swimmers
2.1 Cichlids (Eartheaters, South/Central Americans, Africans) and their derivatives (KKP, parrots, Flowerhorn/LH)
These tend to be fast moving, and tend to snatch food from aros. As long as they are not aggressive towards the aro, they can be considered as good companions.
As all cichlids and their derivatives are aggressive by nature, choose smaller specimens that do not show aggression to the aro. Try to avoid the ultra aggressive types such as Parachromis Dovii, Caquetaia Umbriferus.
Cichlids are good tank cleaners as they can eat up the leftovers in the tank.
Discus and angels can beautify the tank, however, they can be easily targeted by an aggressive aro. Nevertheless these have been kept with aros successfully before.

2.2 SBKM
Fast moving, tend to snatch food from aros, mid water swimmers, grow very fast, they can be used to distract the aro (disperse aggression). However, they easily outgrow the aro and therefore cannot be a long term tankmate.

2.3 Snakeheads
Surface to mid water swimmers, may threaten small aros, distract aro (disperse aggression) Most snakeheads, when mature tend to be very aggressive, hence, they are suitable tankmates only for short term and it is safer to keep bigger aros with smaller snakeheads, and not the other way around.

2.4 Silver Dollars, Red Hooks, Emperor Hooks, Pacus
These may nip the fins of the aro, to prevent such occurence, ensure food is adequate for them. They are fast swimmers, and most have silvery scales that distract the aro causing a dispersal of aggression especially in a small aro community tank. They are not very efficient in cleaning tank of leftovers as they do not eat a lot.
Kelahs can be food for the aro, therefore keep larger specimens as they grow slow in the tank and easily become the aro's target.

2.5 FF (Semaprochilodus taeniurus)
May nip fins of aros, they are fast swimmers, can distract aro (disperse aggression), and in addition is able to clean the tank of algae. They are very jumpy fishes and only one FF can be kept in a tank as they are extremely destructive towards conspecifics (same species).

2.6 Gars
Only spotted gars can be appropriate tankmates. Alligator gars, Cuban gars tend to be too aggressive. Nevertheless, most gars grow very big, and are therefore not good tankmates over the long term. They also have long snouts and swing their snouts to catch food. Their teeth may hit the aro's eyes.

2.7 Datnoids
Siamese Tigers, Indonesian Tigers, New Guinea Tigers, American Tigers, Northern Thailand Tigers are all appropriate tankmates and can be pleasing to the eye, however, some can also be very aggressive towards an aro.

Tigers 'pop' & snatch food very fast, and big ones would definitely spook a smaller or same-sized aro. NGT known to be the fiercest of the lot.

2.8 Majestic Shelter (Distichodus Sexfaciatus)

Nice tankmate for aro. Not aggressive to other tankmates. Chased by my ITs but never chased them back even those that are smaller in size. Not fussy with food and are very good at clearing leftovers (SWs, pellets and MPs). Tend to snatch SWs from Aro. The major plus point is, my MS is very hardworking at clearing the "snowflakes" (the shattered SWs when Aro chews them). It actually goes for the scattered individual "snowflakes".

2.9 Dorados, ATF, Payara
These are predators that will only take live food. Dorados and African Tiger Fish are swift swimmers, and can also be aggressive when they mature. Some attention needs to be paid on feeding as they compete with aros for food. Also watch that your aro is not spooked by their swift swimming stunts in the tank.

dorado:
they grow very fast n eat a lot. can grow up till 3"/mth for juveniles before slowing down at ard 10-12".
also a very fast n aggressive fish. need to drop food near aro but they r capable of snatching food right infront or off aro's mouth.

2.10 Monodactylus Sabae

Very active, Chasing foods (Mp, small feeders, small frogs), fast swimmers, but not so well if you are keeping Rays (Slow swimmer tank mate e.g : Catfish, etc..) as they're fin-nippers. These grow into very impressive pieces with long outstretched fins like a bat.

2.11 Tin Foil Barbs, Kelahs

TFBs provide a good and stable partner in the tank, Kelahs is a more variable mix to an arowana tank. They grow slow and some are quite rare in the hobby. Kelahs have been successfully introduced into aro tanks without problems.