In general, choose tank maintenance crews that are alert and agile. They are most likely to survive and also most likely to do their jobs in open areas, instead of hiding all the time.

Algae and pest eaters that work for me:

• Siamese Algae Eaters – Very agile, active and alert. Algae nibblers that are good for hair-like algae such as Black Beard Algae, Hair Algae and Thread Algae. Still excellent as adults because they don’t get fish food and so continue to graze actively for algae. However, they may feed on some plants.
• Panda Garras – Very hard-working, active, alert and entertaining. Algae scrapers that are good for flat algae like Green Dust Algae and Green Spot algae. They are constantly scraping algae. Territorial among themselves, so you can’t have too many. Reported by some to go after the slime coat on large fishes. In my case, 1 out of the dozen or so I have had went after the Arowana’s slime coat and wouldn’t give it up, so I had to remove it.
• Dwarf Chain Loaches – Very hard-working, active and entertaining. These excellent fellas help to control the snail, worm and planaria populations. I had a minor planaria infestation which disappeared about 2 weeks after I added these fellas. Similarly, I don’t see the earthworm-like worms when I vacuum my substrate nowadays. The small snails are still around but under control. These guys are also small enough that the full-grown Arowana doesn’t bother with them at all.

What should be avoided:

• Plecos – These fish have spines and can get stuck in the mouth/throat of the Arowana if it attempts to eat them. On a personal note, many species are nocturnal and/or shy, so they tend to hide a lot.
• Otocinculus – Similar to plecos, Otos have spines and might get lodged in the mouth/throat of smaller Arowanas. They also tend to zone out and stay stationary, which makes them attractive targets to catch.
• Snails – I have witnessed both my Arowanas eat snails, so they are unlikely to survive long. Besides that, the Nerite Snails and Porcelain Limpet Snails (Septaria porcellana) lay their eggs all over hard surfaces and are pretty hard to remove. And if you have Trypophobia, their eggs are going to trigger you.

It depends. I’ve seen a video of a tank with a rock and plant feature in one half of the tank, and a tree-like driftwood with attached plants in the other half, on an otherwise flat plain of carpet plants. There was a stressed-looking school of Neon or Cardinal tetras swimming to and fro between the rocks and driftwood as the arowana glided from end to end of the tank. On the other hand, in the same video, there were Yamatos and Otocinclus calmly and happily grazing among the plants and clinging to the hardscape and glass.

In my own tanks, the small tank mates are constantly alert and cautious, but do not look stressed to me. From my observation, if you provide ample havens with plants and hardscapes where the small fishes can retreat to, they are less likely to be stressed by fear. They know they have places where they can rest and hide safely and out of sight and will instinctively balance the risk between safety and feeding.

It is usually in the first 48 hours that newly added fishes are the most stressed. They are new to the tank and have no idea where to hide. Their instinct is to hide in the corners of the tank, in which they have few avenues of escape when the Arowana comes for them. The Arowana is also able to recognise that they are new and lost, and will actively hunt them. When I add new small fish, I make sure to put obstacles in the tank corners that block the Arowana and allow the new fish to hide behind. I also recently noticed that the, now adult, Arowana can’t be bothered to hunt very small fishes and it ignored the 1-inch slivers of juvenile SAEs when I added them. By the time they get big enough for him to bother with, they already know how to keep their distance and where to hide.

In a simple sentence: Yes, if they fit in its mouth and are easy to catch.

Do not put in any small fish that you are not prepared to lose. The arowana is a predatory fish after all. My current arowana has taught me that it differs from fish to fish. I have never seen my previous arowana actively hunt down its tank mates. However, my current one, given the opportunity, will try to eat the tank mates. That said, the tank mates do not offer many opportunities for it to do so. As long as he thinks they are alert, he doesn’t bother to waste energy on them. But if the spots an inattentive one, he will try. He also pokes his head into the plants sometimes, if he spots one zoned out under the leaves.

The following will greatly help:

1. A lushly planted tank provides lots of cover and the prey are smart enough to when to hide and when they can be in the open.
2. The same smart prey knows how to stay away from the jaws of death. My SAEs, Panda Garras and Dwarf Chain loaches swim and feed in the open almost all the time. They are alert but not panicked and will keep their distance. They can tell when the Arowana is targeting them and when he isn’t.
3. Most predators will not expend unnecessary energy to catch their food. If your arowana gets fed regularly and fed well enough each time, it would wait for the easy food and not bother to chase difficult food.

Tips

• If possible, get an arowana that was trained from young to eat non-live food. Like pellets and market prawns.
• Keep middle and bottom swimmers. Arowanas have upturned mouths which are designed for prey swimming near or on the surface and hanging off plants above water. An aggressive arowana may still try to eat such tank mates but is not well equipped to do so.
• Keep fishes that are agile and fast.
• Do not keep too many other fishes.
• Big Arowanas will ignore very small fishes. My Arowana is currently 22 inches long and he ignores the slim 1-inch Dwarf Chain Loaches.
• Do not keep any fish or other tank makes that have spikes, thorns, poison, etc. E.g. Otocinclus and snails with spiky shells (I have seen my first arowana chomping on tiny snails a couple of times).

Large Fishes

Fish that are too large to be eaten are safe from the arowana. However, you may want to consider whether your arowana is safe from them. Also, a planted tank needs to maintain comparatively low levels of Ammonium/Ammonia, Nitrites and Nitrates. Having a high fish load would make it difficult to keep the algae away.

Possible, but unlikely, if you scape wisely. Arowanas are large, active and powerful fishes. Aggressive ones may try to chase and eat their tank mates. When frightened, the arowana, like most fishes, may dart away suddenly and in some cases, blindly. Scape so that:

1. The hardscape is unlikely to be in the way, and
2. If they do knock into the hardscape, injury is minimal.

Rocks can be used in the lower part of the scape. Use rocks with smoother surfaces instead of very rough ones or ones with sharp knife-like edges. Use roundish rocks rather than pointy rocks. For wood, instead of placing them to stick up like branches, place them so that the sharp pointy bits point are buried in the substrate, like exposed roots of trees. Try to keep most of the hardscape below half the tank. Use soft plants with tall long leaves to fill up the upper spaces at the sides or back to balance the scape.

My first arowana was a juvenile, about 8 inches long when I introduced it to my planted tank. It adapted well and never tried to purposely remove or destroy the plants. There are many other people who successfully keep arowanas in planted tanks.

My current arowana was also introduced into a fully planted tank as a juvenile. It is mostly living peacefully with the plants.

The main cause of plant damage by my arowanas is when they try to eat a fish that was resting on a large leaf or trying to escape through some plants. My current red, though, has been observed trying to remove some of the taller plants in its way. So far no significant damage caused by either fish that are obvious.

As far as I know, Arowanas do not make “nests” like some species of Cichlids and other fishes, hence will not instinctively try to move your tank contents around. However, I have read a few posts where plants were introduced into the tank of an adult arowana which had been living in the same bare tank for many years. Those arowanas did not like the intrusion and pretty much destroyed the plants.

My personal take: if you have an older arowana that has been living in the same bare tank for many years, then you will have to test its tolerance with a few cheap plants on wood or in pots first.