All fish lovers treasure the Siamese algae eaters for their vital role in community aquariums. They assist in getting rid of unwanted/adamant algae growths, which refuse to go.

Siamese algae eaters are peaceful and easy to care for, which qualifies them as perfect candidates for any community aquarium. Many beginners and experts add them proactively to enjoy the perk of having algae-free tanks. However, there are caveats to keeping them happy and healthy in home aquariums.

They are often confused with other similar-looking fishes, which do not perform the same role, causing disappointment.

We will learn everything about Siamese algae eaters in this article; so you choose the correct species and provide them with the best care.

Species Overview

Generic facts
Scientific Name Crossocheilus Oblongus
Other popular names Siamese Algae Eater (SAE)
Family Cyprinidae
Origin Mainland Southeast Asia
Life Span Up to 10 years
Adult Size Up to 6.3 inches
Type Freshwater

Origin and Habitat

Thailand was known as Siam in older times. Hence, these species originating from Southeast Asia are known as Siamese algae eaters, combining their origin and eating habits.

They thrive in river beds of Malaysia and Thailand, including the Mekong River, which runs through east and Southeast Asia. However, experts breed them globally to meet the rising demand.

Their natural environment consists of slow-moving to still waters in the river depths having thick plantations, rocks, and caves that provide ample food (algal growth) and double up as ideal hiding/resting spots.

During the rainy season, they move to flooded forests.

Siamese Algae Eater Size and Lifespan

They grow up to 6 inches within two years. With good care, their life expectancy is up to a decade in captivity.

Physical Appearance

Photo Credit (2023, January 21). CC BY-SA 4.0, In Wikipedia.

They have slim, long bodies that are grey or golden. A bold, black line runs horizontally through the center of their bodies from the mouths to the end of the tail fins. The borders of this line are serrate/rough.

The upper halves of their bodies are darker than the lower halves. Scales on the upper bodies have a black border on each of them, highlighting them neatly.

They have a dorsal fin (on the upper bodies), a pectoral fin, a pelvic fin, and an anal fin on the lower bodies. All four fins are transparent rays-like, with lines running through them. Their transparent forked tail fins have horizontal lines running through them.

A pair of barbels/whiskers on the lower jaw helps them scavenge. The above image shows a Siamese algae eater searching for algae on a snail.

Importance in Aquarium

Several fishes eat algae. However, they do not eat the black beard algae (also known as BBA, black brush, or red algae). It’s the toughest algae to clear in any aquarium.

Siamese algae eaters are the only species that eat all types of algae, including the black beard algae, making them highly desirable for ongoing and effective algae check.

Typical Behavior Patterns

  • In the wild, they live in small groups and prefer known places. Do not swim away in search of newer pastures.
  • In captivity, they can stay alone with other fishes. Some may become aggressive with the same species till they settle.
  • Siamese algae eaters are jumpers and may jump outof the fish tank. Always cover the community tank properly.
  • They prefer to stay at the bottom level and are active throughout the day. However, they can swim at other levels to eat algae (on glass/floating).
  • They do not have swim bladders. Hence, they cannot balance themselves in the water.
  • So, these algae eaters constantly swim to avoid falling to the bottom. It explains their high activity levels.
  • Do not worry if they swim weirdly sometimes. As long as they are swimming, they are fine.
  • They rest on plant leaves, rocks, or inside caves when tired.
  • The black stripe on their bodies disappears/fades out when in stress or, to camouflage in the environment, when in danger.
  • They are not fussy about food.
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Sexual Dimorphism

They cannot be distinguished gender-wise until they are sexually mature. Around 3-4 years of age, adult female fishes look rounder in the bellies than their male counterparts (when seen from the top). They are approximately 30% larger than males.

Siamese Algae Eaters Vs. Flying Fox

Several species are sold in the fish trade as Siamese algae eaters. It is due to a lack of proper knowledge of a few vendors/buyers. These species are saleable when they grow one to two inches and look similar in juvenile years.

The most commonly confused species are the flying fox and the false flying fox.

Many use the term true Siamese algae eaters interchangeably. These species also eat the BBA (refer to section 1.4) but differ slightly (like scientific names and sizes). Besides, genuine species of this kind with no whiskers and well-protruding, v-shaped upper lips are rarely available in trade.

Below are the images of all four species, followed by a table listing the main differences in adult fishes. They all originate from Southeast Asia.

Siamese Algae Eater (Crossocheilus) Image [email protected] Wikipedia.
True Siamese Algae Eater
Flying fox fish image [email protected] In Wikipedia.
False Flying Fox (Cambodian logsucker) Image [email protected]
Details Siamese Algae Eater True Siamese Algae Eater Flying Fox  Fish False Flying Fox
Scientific Name Crossocheilus Oblongus Crossocheilus Siamensis Epalzeorhynchos Kalopterus Garra Cambodgiensis
Genus Crossocheilus Crossocheilus Epalzeorhynchos Garra
Popular Names None None Siamese flying fox Cambodian logsucker, Stonelapping minnow, False Siamese algae eater.
Adult Size (Max.) 6.3 inches. 12 – 15 inches. 4.7 – 6.0 inches. 5.9 inches.
Eat Red/Beard Brush Algae Yes. Yes. No. No.
Eat Other Algae Yes. Yes. Yes. Yes.
Fins Transparent. Have coloration.
    A unique red marking on the lower body line between the anal and tail fins.  
Thick Black line in Central Body A lateral line from the mouth to the end of the tail fin. A horizontal line runs from the mouth to the start of the tail fin.
Rough/zig-zag borders. Smooth borders.   A golden line above the upper border.
Upper Body Comparatively lighter than the lower body. Relatively darker than the lower body.
Scales on upper Bodies Clear with black outline/lining. Not clear or demarcated.  
Sexing Possible only in adults.  
Females are plumper from the center than males.
    During spawning:   Both develop tubercles on the snouts.  
Males get a red tinge under their mouths.
Flap in Front of the Mouth No. No. Yes. No.
Has Barbels/Whiskers Yes, a pair on the lower jaw. Yes, a pair on each jaw. Yes, a pair on each jaw.
Temperament Peaceful. May become territorial with the same species initially. Aggressive.

Availability and Price

They are available in local fish stores and online. They are saleable from one to two inches in size. Use the correct scientific name while purchasing.

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Seek information on possible adult fish image, maximum size (in the future), and check the distinguishing features (refer to section 1.7). Ask if they will eat the red algae.

A Siamese algae eatercosts from $4 onwards. The pricing varies according to size, availability, origin, offers, and quality. Always buy from a reliable and knowledgeable source.

Siamese Algae Eater Care

Care Overview
Care Level Easy
Diet Omnivorous
Temperament Non-Aggressive. May get territorial with the same species initially
Breeding Egg layers. Difficult in Captivity
Social Gel well with other fishes
Tank Level Bottom Level

Siamese Algae Eater Food

True to their name, they are voracious algae eaters. They also eat plankton and decaying organic matter (like plants, leaves, dead fish, etc.) in the wild. Although omnivorous, they are not predators.

How and What to Feed

They accept any fish food (live, frozen, veggies, pellets, flakes, etc.). However, their diet should be mainly vegetarian.

Feed them once or twice a day in small portions for two minutes. Use sinking foods or slightly moistened foods that can reach these bottom dwellers.

Use high-quality food and serve various foods in rotation to provide nutrition. De-freeze frozen food before feeding.

Siamese algae eaters keep eating algae and plankton the whole day. In addition, they scavenge and eat uneaten food at the tank bottom. Hence, do not overfeed them. Skip feeding them once a week if need be.

They may nibble on plants indicating no/insufficient algae/biofilm in the aquarium. Provide them with supplementary foods.

The flip side of providing other foods regularly is that they may develop a preference for them and stop eating algae, killing their very purpose in the aquarium. Observe their growth, coloring, activity, etc., and decide on their diet.

Offer them Spinach, Zucchini, Peas, Algae wafers, live/frozen Brine shrimp, Bloodworms, Fish Pellets/Flakes, etc.

Breeding Siamese Algae Eaters

Siamese algae eaters lay eggs. Many hobbyists have reported the breeding behavior of their pair chasing each other. While tagging each other, the male fish rubs the swollen belly of the egg-bearing female fish. However, there are no official reports beyond this about successful breeding in any aquarium to date.

Details of how they breed in the wild are a mystery (like the breeding season, gestation period before laying eggs, the timeline for hatching eggs, growth stages, etc.).

There is similar information available on a few other algae-eating species. They breed during the rainy season in the flooded forests and take care of the frys before returning to the river bed after the rainy season.

Aquaculturists breed them commercially in aqua farms/ponds using hormones to induce spawning. The exact details (like the water parameters, number of injections administered to each gender, number of eggs per spawn, growth rate/stages of frys, etc.) are a well-kept secret.

Induced spawning can be semi-natural or artificial. Learn more about fish spawning and fish fry care in general.

Unfortunately, you may not be able to breed them in a community tank. If you do, please share more details. We await success stories.


Siamese algae eaters are sturdy. However, the community tank needs to be well-maintained to keep them healthy.

The most common disease found in them is Ich (also known as Ick, White Spot Disease, or Ichthyophthiriusmultifiliis).

Learn more about this and other common diseases in aquarium fishes, their symptoms, and ways to prevent them.


Quarantine every new fish to ensure no bacteria/parasites enter your tank.

Acclimate the new fish to your aquarium water parameters; so it gets accustomed to your aquarium water and adjusts to the new environment with the least stress.

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Tank Size and Water Parameters

 Tank Requirements Overview
Minimum Tank Size 20 Gallons
Water Temperature 75 -79° F /24 – 26° C
pH Level 6.5 – 8.0
Water Hardness 5 – 20 dH

Tank Size

A 20-gallon tank is just enough for a single algae eater. It is advisable to have a 25-gallon tank to allow sufficient free space. Consider 10 gallons/per additional fish.

As discussed earlier, you can add a single Siamese algae eater or a group of 2 or more. Chances are that you already have a community tank with the choicest of fishes and need help with algae growth.

Depending on the extent of algae growth and available free space in your community tank, decide on how many you can add. Do not overcrowd the aquarium.

Tank Setup

Tank setup is an opportunity to recreate an environment that closely resembles the original habitat of tank dwellers. Accordingly, Siamese algae eaters prefer a well-planted aquarium having enough algae and hiding/resting places to feel happy, healthy, and safe in captivity.

Everything that enters the tank should be sanitized and have smooth edges/surfaces. Any opening in the tank should be wide enough for the fishes to swim through them without hurting/getting stuck. You may also need a heater to maintain the water temperature if need be.


Live plants promote algae growth in light and also keep the aquarium well-oxygenated.

Siamese algae eaters may eat the plants, if there is no food. But they do not damage the plants. Add fast-growing plants (like Hornwort and MarsileaHirsuta), plants with large leaves to hide/rest (like Anubias, Water Lettuce, Tiger Lotus), Java Moss, Java Fern, Amazon Sword, etc.


A soft substrate is apt to protect the Siamese algae eaters while scavenging. Choose a substrate with soil that promotes plant growth and facilitates scavenging instead of a substrate where food particles get stuck deep in the gaps.


Use decorations that can provide resting places at mid and bottom levels in the aquarium. Decors like rock, driftwood, bogwood, and caves are apt, where they can hide away from their tank mates. Besides, algae growth on the decorations can become food sources.

Driftwood and botanicals release tannin (a chemical), which makes the water acidic and promotes algae growth.

Be creative to make your aquarium colorful and aesthetically pleasing.


Siamese algae eaters need a day-night cycle. However, the light penetrating the river bed is soft. Accordingly, you do not need any specific bright light. Remember, thickly planted aquariums need sufficient light for the plants for photosynthesis. Plankton and algae need light to grow.

Oxygen and Filtration

The aquarium water needs to be sufficiently oxygenated. Considering you need to cover the tank lid, the only way to provide oxygen inside the aquarium is through an air pump and air stone.

Use a filtration system apt for the tank size to keep the water clean. While the Siamese algae eaters eat decaying organic matter, you will still need to remove a lot of it from piling up, as it will deteriorate the water quality.

Perform 10-15 percent partial water changes once a week. Maintain/clean the oxygen and filtration system periodically for best results.

Keep the water current slow-moving to reflect their natural habitat.

Siamese Algae Eater Tank Mates

Ideal tank mates should be non-aggressive. Fishes that can feast on them should not be kept in the same tank. Siamese algae eaters do not eat live fish. They only eat dead fish.

Thus, Gouramis, Neon Tetras, Danios, Swordtails, Freshwater Snails, Angelfish, Barbs, Corydoras, Galaxy Rasboras, etc., make good tank mates.

Frequently Asked Questions (FAQs)

How to know if a Siamese algae eater is dying?

Siamese algae eaters are active species. You will always see them in action, despite being bottom-dwellers.

Many of them die in aquariums of starvation. It typically happens when they are added proactively without any algae problem. Or too many of them are added, and the aquarium has very little algae growth to feed all.

Many new fish owners assume that adding them means they will auto-feed on algae and fail to feed them supplementary food if there is no/inadequate algal growth.

Your algae eater will lose weight and look pale/faded in color. They will lack enough energy to move around, fall to the bottom, and stay there. Its eyes may become cloudy. Eventually, they will die and not respond to any stimuli once dead.

They may lose appetite and fade in color if unwell. Identify if they have any diseases. Consult a fish expert for correct diagnosis and treatment. Besides, if they have been with you for a decade or more, death is inevitable with the above tell-tale signs. Comfort them as much as possible after checking with your fish vet.

Can I add Siamese algae eaters with my betta fish?

Yes. Siamese algae eaters will be safe in the same tank with your betta fish. They are the best algae cleaners for your fish tank. Both can co-exist.

Final Thoughts

Are you already considering adding a Siamese algae eater? That is great! There is no harm in adding one proactively. It will keep the bottom level of your aquarium abuzz with its constant activity.

You will forever be thankful to have a successful algae-free aquarium for a decade with very little investment.

Now that you are an expert on them, we wish you a happy fish parenting time!

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About the Author

Victoria Lamb

Victoria is a freshwater aquatics specialist, fish keeper, and amphibian enthusiast. She has had more than 6 years of experience caring for aquariums and keeping several fish species, and her home boasts of 3 aquariums and a garden pond. Her goal is to educate fish owners on raising healthy and happy aquatic pets. Career Highlights:…

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