Thread-finned acara Care Guide: Diet, Tank Mates, Diseases, Breeding & More

Updated: December 17, 2022

The Thread-finned acara (Acarichthys heckelii) is a beautiful and peaceful freshwater fish that is perfect for the community aquarium.

They are not aggressive and get along well with other fish, making them a great addition to any tank.

Thread-finned acaras are also easy to care for and are not picky eaters. In this guide, we will go over everything you need to know about Thread-finned acara care.

Species overview

The thread-finned acara (Acarichthys heckelii) is a freshwater fish that’s native to South America. It’s found in the river basins of the Amazon, Orinoco, and Paraná.

This fish prefers slow-moving waters with a lot of vegetation. This is something that’s common to many South American freshwater fish, as the continent is home to a large number of rainforests.

The thread-finned acara is a peaceful fish that’s compatible with a wide variety of tank mates. It’s a popular choice for many aquarists due to its bright colors and interesting appearance.


Thread-finned acara

The Thread-finned Acara is a beautiful freshwater fish that is easily recognizable thanks to their long, thin, and colorful fins.

The body of this fish is fairly thin and elongated. They have a small head with large eyes that sit just above their mouth. The mouth of the Thread-finned Acara is fairly small and pointed downwards.

This fish has a small dorsal fin that is located just behind their head. Their anal fin is located further back on their body and is roughly the same size as their dorsal fin.

The caudal fin of the Thread-finned Acara is large and forked. This fin makes up a large portion of their body and is where their name comes from.

Their pectoral fins are located just behind their head and are thin and long.

The Thread-finned Acara is a very colorful fish. They have a base color that is usually some shade of blue or green. This color is then adorned with spots, stripes, or other patterns that can be quite beautiful.


The average lifespan of a Thread-finned acara is around 10 years. This is a long time for a fish and it’s a testament to how hardy they are.

Of course, there are a number of factors that can impact their lifespan. If they’re kept in poor water conditions or with aggressive tank mates then their lifespan will be significantly shorter.


The average size of a Thread-finned acara is around 4 inches, but they can grow to be up to 6 inches long.


Tank Size

The recommended tank size for a single thread-finned acara is 30 gallons. If you’re looking to keep a pair of fish, you’ll need a tank that’s at least 50 gallons.

While these fish aren’t the largest on our list, they are known to be pretty active swimmers. They also like to dig and will often rearrange your substrate. For these reasons, it’s important to give them a little extra space to roam.

Water Parameters

Acara are a little bit more delicate than some of the other freshwater fish on this list. They need very specific water parameters to stay healthy and thrive in captivity.

The most important thing to remember is to never make sudden changes to the water parameters. These fish are very sensitive to changes and can easily succumb to stress.

If you need to make a change, do it gradually over the course of a few days. This will give the fish time to adjust and reduce the risk of stress.

Here are the ideal water parameters for thread-finned acara.

  • Water temperature: 75 to 82 degrees Fahrenheit
  • pH levels: 6.8 to 7.6
  • Water hardness: 5 to 15 dGH
  • Alkalinity Levels: 4-8 dKH

What To Put In Their Tank

The inside of their tank is just as important as the outside. A comfortable fish is a happy fish, and a happy fish is a good fish.

When it comes to the substrate, these fish aren’t very picky. You can use standard gravel if you wish, but we prefer sand if you can manage it. Since they will spend a lot of time at the bottom of the aquarium a softer substrate will be a little nicer for them (they might even do a bit of digging in it).

Something that you should definitely include in a tank with a Thread-finned acara is a decent piece of driftwood. These fish love to spend time hiding underneath logs and wood (especially during the day). Not only that, but wood is a great surface for algae to grow on which will give them something to snack on as well.

Don’t go overboard when adding wood to their tank. One or two solid pieces if you have a 100-gallon tank should be fine. If you’re keeping them in something significantly larger feel free to add more though!

You can also add some plants to their habitat as well. Leopard Plecos are known to nibble on vegetation so you’ll want something that can bounce back (Hornwort, Water Wisteria, or Java Moss are all great choices). Don’t feel obligated to go with a heavily planted tank for this species though.

Common Diseases

The Thread-finned acara is a hardy and relatively disease-resistant fish. However, that doesn’t mean they can’t get sick.

The most common disease that affects this species is ich. This is a parasitic infection that will present itself as white spots on the body of your fish.

If left untreated, ich can be fatal. However, it is relatively easy to treat with medication (you can find these at your local pet store).

Another disease to look out for is hole-in-the-head disease. This is a condition that is caused by poor water quality and the presence of activated carbon in your tank.

This will present itself as one or two pits/holes in the skin of your fish’s head. While it’s almost always curable (fixing your water quality and removing activated carbon is usually all you need to do), it will usually leave some scarring on your poor fish!

As always, the best way to prevent these diseases is to maintain a clean and stable tank. This will keep your fish healthy and make them much less likely to get sick.

Behavior & Temperament

The thread-finned acara is a beautiful but shy fish. It’s not uncommon for this fish to spend most of its time hiding behind plants or other objects in the tank.

The thread-finned acara is a peaceful fish that gets along with other fish. However, it can be aggressive towards fish that are similar in appearance to itself.

This fish is a bottom-dweller and spends most of its time scavenging for food. It’s an active fish and is constantly on the move.

The thread-finned acara is a timid fish that is easily scared. It can be skittish and may be stressed by too much activity in the tank.

Tank Mates

Tank mates for a thread-finned acara should be chosen with care. These fish are not the most peaceful, and they can be quite aggressive at times.

They’re also territorial, which means they might not do well with other fish that occupy the same space in the water column.

For these reasons, it’s best to choose tank mates that are either much larger or much smaller. This will help to reduce the chances of aggression.

Some good thread-finned acara tank mates include:


The thread-finned acara is a relatively easy fish to breed in captivity. These fish are egg-layers and will lay their eggs on just about any surface.

To start the breeding process, you need to set up a separate breeding tank. This tank should have plenty of hiding places and be well-filtered. The water should be soft and acidic. Aim for a pH of 6.0 and a hardness of 2 to 4 dGH.

Once the tank is set up, you can add a pair of fish. These fish will usually start breeding on their own. If they don’t, you can try to trigger spawning by raising the water temperature. Aim for 84 degrees Fahrenheit.

When the female is ready to lay her eggs, she will do so on a flat surface. It can be a piece of driftwood, a rock, or the glass. The male will then fertilize the eggs.

After that, the parents will guard the eggs until they hatch. This usually takes about 10 days.

Once the fry hatch, you can remove the parents. The fry will feed on microscopic organisms in the water. You can supplement their diet with baby brine shrimp or other small live foods.


Thread-finned acara care is not difficult, but there are a few things to keep in mind.

First and foremost, these fish are predators. This means that they will likely eat any smaller fish that they come across.

While they can be kept with other fish their own size, it’s generally best to keep them alone or with fish that are significantly larger.

Another thing to keep in mind is that these fish are not the most active. They’re not going to swim around a lot, so don’t expect them to.

Overall, we think the thread-finned acara is a great choice for someone who wants a low-maintenance fish that is still interesting to look at. Just be sure to do your research and make sure they will be compatible with the other fish in your tank!