Siamese Algae Eater: Natural Tank Cleaner

The Unsung Hero of the Freshwater Tank

If you’ve ever owned a planted tank, you probably know the eternal struggle—algae. No matter how often you clean the glass, trim your plants, or tweak your lighting, the green film always seems to come back. That’s where the Siamese Algae Eater steps in, not as a flashy centerpiece fish, but as the quiet janitor of the aquarium world. It’s not the most colorful fish in the tank, but its work ethic is second to none.

FISH PROFILE
Fish:	Siamese Algae Eater
Binomial Name:	Crossocheilus oblongus
SCIENTIFIC CLASSIFICATION
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cypriniformes
Family:	Cyprinidae
Subfamily:	Labeoninae
Genus:	Crossocheilus
Species:	C. oblongus
Varieties:	N/A
ENVIRONMENT
Living Environment:	Freshwater
Found in:	Thailand, Malaysia, Borneo, and parts of the Mekong River basin
Space Requirement:	At least 30 gallons (113 liters) per fish
Average Lifespan:	8–10 years
Exceptional Cases:	Up to 12 years in optimal conditions
Length:	Up to 6 inches (15 cm)
Weight:	Approximately 20–30 grams
Temperature:	24–26°C (75–79°F)
pH:	6.5–7.0
PERSONALITY
Temperament:	Peaceful when young, may become territorial with age
Social Behaviour:	Best kept in small groups of 4–6 to reduce aggression; active mid-bottom dwellers
Diet:	Omnivore
Food Type:	Algae, biofilm, sinking pellets, blanched vegetables (zucchini, spinach), and occasional live foods
KEY FACTORS AFFECTING LIFESPAN
Enclosure / Tank size:	Requires a spacious tank (minimum 30 gallons) with ample swimming space and hiding spots
Habitat / Water quality:	Prefers clean, well-oxygenated water with good flow; sensitive to poor water quality
Diet:	Balanced diet including algae and supplemental food prevents malnutrition and stress
Companions:	Compatible with peaceful community fish; avoid aggressive or fin-nipping species
Temperature / Environment stability:	Stable temperature and water conditions are essential for long-term health
CARE DIFFICULTY
Difficulty Level:	Moderate
Messiness:	Low to moderate; produces minimal waste but requires good filtration due to algae debris
Additional Requirements:	Needs moderate water flow, quality filtration, oxygenation, and a secure lid to prevent jumping
Special Notes:	Highly effective algae cleaner; ensure it’s not confused with similar species like the Flying Fox

Native to the slow-moving rivers and streams of Thailand, Laos, and Cambodia, the Siamese Algae Eater (Crossocheilus oblongus) is a freshwater fish that thrives in warm, well-oxygenated waters filled with plants, roots, and submerged wood. In the wild, it spends most of its day scraping algae from rocks and plants. You’ll often find them swimming against the current, nibbling endlessly, like tiny aquatic vacuum cleaners.

In home aquariums, these fish quickly earn their keep. Many aquarists—especially those with lush planted tanks full of Java Ferns, Anubias, and Amazon Swords—swear by them as one of the most effective natural solutions for algae control. They’re tireless grazers, working through thick carpets of algae that other fish ignore. Even Otocinclus catfish or Amano shrimp, both known algae eaters, can’t match their stamina.

Still, the Siamese Algae Eater is often misunderstood. Many pet stores mistakenly sell Flying Foxes (Epalzeorhynchos kalopterus) or Chinese Algae Eaters (Gyrinocheilus aymonieri) under the same name. These imposters may look similar at first glance, but their behavior couldn’t be more different. Flying Foxes grow more territorial with age, while Chinese Algae Eaters can become aggressive and latch onto other fish. The true Siamese Algae Eater, in contrast, remains peaceful and community-friendly throughout its life.

Their appearance is deceptively simple—slender silver body, horizontal black stripe from nose to tail, and clear fins. No metallic sheen, no flashy color morphs. But under good lighting, that dark stripe shimmers faintly with bronze or gold tones. Watch closely, and you’ll notice how gracefully they move, darting from leaf to leaf, always curious, always busy.

What’s endearing about them is their personality. They’re not shy, yet they don’t seek attention. They’ll explore the tank together in loose groups, each fish focused on its task. There’s a quiet rhythm in the way they work, like a well-rehearsed cleaning crew. Sometimes you’ll catch one resting on a driftwood branch, balancing like a bird on a perch, just taking a short breather before getting back to work.

Their value goes beyond algae control. A healthy Siamese Algae Eater helps maintain ecological balance. By consuming algae and leftover plant matter, it prevents waste buildup and improves oxygen exchange on plant surfaces. In simpler terms, it keeps your water cleaner without you lifting a finger.

For aquarists who prefer natural harmony over constant chemical tweaking, this fish feels like a gift from nature itself. You can almost sense it restoring order—quietly, efficiently, and without drama.

In a way, it reminds me of the Corydoras catfish. Both species are small, peaceful, and hard-working. They’re not the stars of the aquarium, but everything looks better because they’re there. The Siamese Algae Eater may not dazzle with color or pattern, but it earns respect through reliability.

Getting to Know the Siamese Algae Eater

Once you’ve brought home a Siamese Algae Eater, you’ll quickly realize there’s more to this fish than its reputation as an algae-eating machine. It’s a fascinating little creature—curious, active, and surprisingly social. But to really appreciate it, you need to understand how to identify the true species, how it behaves, and what kind of environment keeps it happiest.

Distinct Appearance and Identification

Here’s where things get tricky. Many fish labeled “Siamese Algae Eater” at pet stores aren’t the real deal. The true Siamese Algae Eater (Crossocheilus oblongus) has a few subtle traits that help you tell it apart:

A solid black stripe runs from the tip of its nose through the tail fin, not stopping at the caudal peduncle.
Its fins are completely transparent, with no color bands or markings.
It lacks barbels (the small whisker-like organs near the mouth) that the similar Flying Fox has.
When stressed or resting, the black stripe can fade slightly, then darken again when active.

These differences might sound minor, but they matter. Flying Foxes and Chinese Algae Eaters can grow territorial or even aggressive as they age, while the true Siamese Algae Eater remains gentle, even in community tanks. Once you’ve identified the right fish, you’ll know you have a peaceful, hardworking algae eater—not a future troublemaker.

Natural Habitat and Behavior

In the wild, Siamese Algae Eaters inhabit shallow rivers and forest streams across Thailand, Cambodia, and Laos. They thrive in environments with a moderate current, sandy bottoms, and an abundance of aquatic plants. The water there is typically clean, slightly acidic to neutral, and rich with natural algae growth.

They spend most of their time grazing along rocks and submerged roots. You can think of them as underwater goats—constantly nibbling, rarely idle. They swim with smooth, steady movements, gliding from one plant to another, picking off bits of algae or detritus.

In aquariums, that same instinct remains strong. You’ll often find them clinging to driftwood or combing the leaves of Java Moss and Anubias. They’re most active during daylight, especially in tanks with good water flow and open swimming space.

Typical environmental preferences include:

Water temperature: 24–28°C (75–82°F)
pH: 6.5–7.5
Hardness: Soft to moderately hard water
Behavior: Peaceful, shoaling (best kept in small groups of 4–6)

Though often labeled as “bottom dwellers,” they actually use all tank levels. You’ll see them darting midwater, resting on plants, or scavenging along the substrate.

Personality and Compatibility

Personality-wise, the Siamese Algae Eater is one of those fish that just fits in anywhere. They’re active but not aggressive, social but not needy. In small groups, they establish a gentle pecking order without serious fights. Occasionally, two might chase each other around the tank—nothing to worry about, it’s just part of their social play.

They get along well with a wide range of peaceful tankmates. Great companions include:

Cherry Barbs
Pearl Danios
Harlequin Rasboras
Corydoras Catfish
Bristlenose Plecos

You’ll want to avoid pairing them with large or territorial species like Cichlids, Tiger Barbs, or Red-Tailed Sharks. Those fish might harass them or stress them out, especially in smaller tanks.

Interestingly, despite their hardworking nature, Siamese Algae Eaters have moments of calm observation. They’ll hover in one spot, scanning the surroundings like little sentinels. Sometimes, they even mimic the movements of other species in the tank—a behavior aquarists often notice when housed with peaceful shoaling fish like Zebra Danios.

Their peaceful attitude and constant motion make them perfect for community aquariums. They bring life and activity without chaos. Watching a group of them work together feels almost meditative.

Understanding their true identity and natural instincts is key to keeping them happy. A misidentified or mistreated fish won’t thrive, no matter how clean your tank is. But give the Siamese Algae Eater the right setup—a good current, some open space, a few hiding spots—and it’ll repay you tenfold in algae-free glass and healthy plants.

Feeding the Tireless Grazer

The Siamese Algae Eater doesn’t just nibble for fun—it’s built for it. Watch one for a few minutes and you’ll see how it moves with purpose, scanning every surface, scraping off tiny bits of algae invisible to the naked eye. Feeding them right isn’t just about keeping them full; it’s about letting them do what they’re naturally wired to do.

Diet in the Wild

In their native habitats of Thailand, Cambodia, and Laos, these fish spend most of their day grazing on algae, biofilm, and detritus that form on rocks, submerged logs, and plant leaves. They’re opportunistic omnivores—if something edible drifts by, they’ll take it. They don’t rely on prey or large food sources; instead, they thrive on constant, small feedings from their environment.

This grazing behavior explains why they’re so useful in aquariums. They consume:

Soft green algae (the common type that coats glass and plants)
Hair algae, which most fish avoid
Leftover food particles and decaying plant matter
Microorganisms found in the biofilm layer

Unlike some species that eat only when food is added, the Siamese Algae Eater works around the clock. It’s nature’s way of keeping ecosystems balanced.

Feeding in Captivity

In an aquarium, they’ll continue to graze all day, but algae alone won’t always be enough. To keep them healthy and energetic, supplement their diet with a mix of fresh, natural foods and high-quality prepared options.

Good food choices include:

Algae wafers or sinking spirulina pellets
Blanched vegetables like zucchini, spinach, cucumber, or peas
Occasional protein snacks like bloodworms or daphnia
Sinking plant-based pellets designed for bottom feeders

Rotate their diet every few days to mimic the variety they’d find in the wild. That keeps them active and maintains their bright energy. If they lose interest in algae and start waiting for feedings, you may be giving them too much processed food. A hungry Siamese Algae Eater is a working Siamese Algae Eater.

Here’s a quick checklist for balanced feeding:

Feed once daily, just enough to be eaten in 2–3 minutes.
Skip one day each week to let them graze naturally.
Avoid high-fat or meaty foods—they can cause bloating.

You might notice them hovering upside down under driftwood or swimming vertically to reach algae on a filter pipe. They’ll eat anywhere algae grows. It’s one of the few fish that actively cleans surfaces others ignore.

Common Feeding Mistakes

Even though these fish are self-sufficient, aquarists often make a few predictable errors:

Overfeeding commercial food.
Too much pellet or wafer food makes them lazy. They’ll stop eating algae and wait for feedings instead.
Relying on algae alone.
A tank that’s too clean leaves them underfed. They still need vegetables or algae wafers to stay healthy.
Feeding them the wrong food.
Some foods meant for carnivores or omnivores are too rich for their system. Stick to plant-heavy diets.
Not feeding enough variety.
Variety prevents nutritional gaps and keeps them from losing interest in natural grazing.

Many aquarists share the same story: after months of faithful algae control, their Siamese Algae Eater stops cleaning and waits for handouts. That’s not laziness—it’s conditioning. Once they realize food falls from the sky every evening, they’ll start acting like tetras at dinner time. The trick is to let them do their job first, then reward them with something extra.

Feeding these fish the right way is more about restraint than generosity. They’re workers, not freeloaders. When their diet matches their instincts, the result is a spotless aquarium, balanced nutrients, and healthier tankmates.

Watching a Siamese Algae Eater methodically scrape a rock clean while a Bristlenose Pleco joins in nearby is oddly satisfying. It’s like watching two different tradesmen on the same job—each with their specialty, both quietly keeping the ecosystem running.

Ideal Aquarium Setup and Conditions

A healthy Siamese Algae Eater isn’t made by luck—it’s made by the tank you build for it. These fish are energetic swimmers with sharp instincts and a natural love for flowing, plant-rich environments. If you give them the right space and structure, they’ll reward you with years of peaceful movement and relentless algae control.

Tank Size and Layout

A single Siamese Algae Eater needs at least a 30-gallon tank, but groups of three to six should have 55 gallons or more. They’re fast, agile fish that never seem to stop exploring. In small tanks, they can grow restless and may chase each other more than usual.

The layout should mimic their natural environment—a mix of open space and structure. They love weaving through plants and darting under driftwood. Imagine a quiet stream with scattered roots and leaf litter—that’s their comfort zone.

Good decor choices include:

Live plants like Java Fern, Anubias, Amazon Sword, and Cryptocoryne species
Driftwood and river stones to create algae surfaces
Fine gravel or sand substrate to protect their delicate underbellies

Avoid sharp decorations or cramped ornaments. They use every inch of space, and tight corners can cause injuries during their quick dashes.

A useful trick: place flat stones near areas of strong light—algae will naturally grow there, creating a free buffet for your Siamese Algae Eater.

Water Parameters and Filtration

In the wild, Siamese Algae Eaters come from clear, oxygen-rich waters with moderate flow. Replicating that makes all the difference. Keep your tank well-filtered, clean, and stable.

Ideal conditions:

Temperature: 24–28°C (75–82°F)
pH: 6.5–7.5
Water hardness: up to 10 dGH
Ammonia/Nitrite: 0 ppm, as they’re sensitive to toxins
Flow: moderate, with aeration or gentle current from the filter output

They prefer tanks with consistent water movement, which keeps oxygen high and simulates their natural streams. Hang-on-back or canister filters with directional flow work beautifully. If your aquarium has dead spots with little water movement, they’ll avoid those areas altogether.

Regular water changes—around 25–30% weekly—help keep them active and bright. Dirty or stagnant water can dull their color and slow their metabolism.

Best Tankmates for Peaceful Coexistence

The Siamese Algae Eater’s temperament makes it a perfect addition to a peaceful community tank. They don’t nip fins, chase smaller fish, or cause drama. Still, not every species returns the favor.

Excellent tankmates include:

Rasboras (Harlequin, Lambchop, Scissortail)
Barbs (Cherry, Gold, or Odessa)
Danios (Zebra or Leopard)
Gouramis (Pearl or Dwarf)
Corydoras catfish and Kuhli loaches
Plecos (Bristlenose or Rubber Lip types)

Avoid housing them with:

Large or aggressive cichlids (like Oscars or Green Terrors)
Fin-nipping barbs (like Tiger Barbs)
Territorial bottom dwellers (like Red-Tailed or Rainbow Sharks)

Interestingly, keeping them in small groups tends to calm them. A single Siamese Algae Eater may become shy or sluggish, while a group of four or more stays active and balanced. They recognize each other’s movements and often synchronize swimming patterns, especially when exploring new areas of the tank.

Lighting and Algae Growth Balance

Here’s a funny paradox: too much light causes algae, which most aquarists hate—but Siamese Algae Eaters love it. The trick is balance. You want just enough light for your plants and for algae to grow at a natural pace, but not so much that it overruns your tank.

If you run bright LEDs, consider letting them stay on 8–10 hours daily. That’s enough for healthy plant growth and a steady algae supply. Avoid overusing chemical algae removers or UV sterilizers—they’ll take away your fish’s natural food source.

Creating the Right Mood

One of the easiest ways to make them feel at home is to combine natural decor, soft lighting, and steady water movement. You’ll see more natural behavior—grazing in groups, resting under leaves, and exploring during daylight hours.

A planted tank with a good balance of algae, driftwood, and mild current looks not only beautiful but alive. The Siamese Algae Eater thrives in that kind of living, breathing environment.

Give them space, give them flow, and they’ll give you a clean, thriving tank in return.

Breeding and Lifespan in Captivity

For all their resilience and adaptability, Siamese Algae Eaters are surprisingly elusive when it comes to breeding in home aquariums. They’ll clean your tank, coexist peacefully with other fish, and live for years without issue—but getting them to reproduce? That’s another story. Most aquarists go their entire fishkeeping lives without ever seeing it happen. Still, understanding why can help you care for them better and appreciate how special they really are.

Breeding Challenges

In the wild, Siamese Algae Eaters spawn during the rainy season in shallow, slow-moving waters, where the current softens and the temperature drops slightly. The change in environment signals them to breed. Unfortunately, that’s hard to recreate in captivity.

Here’s what makes breeding them so rare in home tanks:

They need large, open areas with clean, soft water and precise flow.
They’re egg scatterers, meaning they release eggs freely in the water column. Without a controlled setup, most eggs get eaten almost immediately.
They likely require hormonal or environmental triggers linked to seasonal cycles—something aquariums can’t naturally replicate.
Their sexual dimorphism is subtle; males and females look nearly identical until fully mature.

Most of the Siamese Algae Eaters available in stores today are commercially bred in controlled farms in Southeast Asia using hormone-induced spawning. These farms use specialized techniques that aren’t practical for home aquarists.

That said, there have been a handful of unconfirmed reports of spontaneous spawning in large, heavily planted tanks—usually when conditions happen to mimic the fish’s natural breeding season. Eggs scatter, fry appear, then vanish as they’re eaten by tankmates or lost in filtration. It’s rare, but possible.

So while you might not breed them at home, you can still ensure they live long, fulfilling lives by focusing on stability, diet, and space.

Lifespan and Growth

Given proper care, the Siamese Algae Eater can live up to 10 years in captivity, sometimes longer. Most aquarists see an average lifespan of 6 to 8 years, which is impressive for a mid-sized freshwater fish.

Growth is steady rather than fast. Juveniles sold in stores are often around 4–5 cm (1.5–2 inches) long, but adults can reach 15 cm (6 inches). They don’t bulk up like some bottom dwellers; instead, they stay lean and streamlined, built for constant motion.

Key factors that influence longevity include:

Consistent water quality: Stable, clean conditions reduce stress and disease.
Balanced diet: A mix of algae, vegetables, and protein keeps their metabolism steady.
Tank size: Cramped environments shorten lifespan due to stress and reduced swimming space.
Companionship: They thrive in small groups and show more natural behavior when not isolated.

It’s easy to tell when your Siamese Algae Eater is happy. They’ll swim actively during the day, graze calmly, and rest occasionally on broad leaves or flat stones. A sluggish or constantly hiding fish usually signals something off in the environment—too much nitrate, poor oxygen flow, or not enough stimulation.

Health and Common Issues

Despite their hardy nature, they’re not immune to stress or disease. The most common issues come from poor water conditions or overfeeding. Their long bodies and active metabolism mean they’re sensitive to toxins that build up in still or dirty tanks.

To keep them in top condition:

Maintain regular water changes (25–30% weekly).
Avoid sharp tank decorations that can tear fins.
Feed sparingly and vary their diet.
Watch for signs of Ich (white spots), a common parasitic infection that appears when water temperature drops suddenly.

When cared for properly, these fish stay lean, alert, and constantly active—traits that make them feel more like living energy than ornaments.

Observations from Long-Term Keepers

Aquarists who’ve kept Siamese Algae Eaters for many years often describe them as consistent companions. They don’t show mood swings or sudden aggression with age, unlike Flying Foxes or Chinese Algae Eaters. Even at eight or nine years old, they’ll still dart through the tank like juveniles, brushing along leaves and checking under driftwood as if it’s their first day.

Some owners say their old algae eaters seem to “train” younger ones by leading them to feeding spots. Whether that’s true intelligence or just patterned behavior, it’s endearing nonetheless.

When you’ve had one for that long, you start to notice its rhythm—when it rests, when it feeds, when it starts its daily route around the glass. They become part of the ecosystem’s heartbeat.

Keeping a Siamese Algae Eater is about patience and balance. You might never see them spawn, but that doesn’t make them any less remarkable. They’re steady, dependable, and long-lived—qualities most aquarists come to admire deeply.

Appearance and Physical Characteristics

The Rainbow Shark is one of the most striking freshwater fish you can keep. Its sleek, torpedo-shaped body shines in shades of dark gray to jet black, contrasted by vivid red or orange fins that give it the “rainbow” name. Adults typically reach about 6 inches (15 centimeters) in length, with males often slimmer and more vividly colored than females.

The fins are the shark’s signature feature—especially the tail and dorsal fin, which glow bright red under aquarium lighting. The body’s dark tone enhances this color contrast, making the Rainbow Shark a true visual standout in community tanks. Juveniles often appear paler, gaining their deep coloration as they mature.

A closer look reveals a flat belly suited for bottom-dwelling behavior, and a pointed snout designed for grazing on algae and detritus. The pectoral fins sit low, allowing for smooth gliding near the substrate. While they look fierce, their “shark-like” appearance comes only from their shape, not their nature. They’re not related to real sharks but belong to the Cyprinidae family, which includes carps and minnows.

Color intensity depends on several factors: diet, lighting, and water quality. A well-fed Rainbow Shark on a balanced, protein-rich diet will show deeper red fins and glossier body hues. Healthy specimens display strong contrast, smooth scales, and clear eyes.

In short, the Rainbow Shark’s combination of dark elegance and fiery fins makes it a captivating choice for aquarists seeking a fish that commands attention without requiring exotic conditions.

Siamese Algae Eater: The Natural Algae Solution