Siamese Algae Eater
Crossocheilus oblongus
Min Tank Size
120L
Adult Size
15.2 cm
Lifespan
10 years
School Size
5+
About
Native to river systems across Southeast Asia, Crossocheilus oblongus is arguably the most useful algae-eating fish you can put in a planted tank. It's one of a very short list of species that will actually consume black beard algae, the stubborn red algae that plagues so many CO2-injected setups. Young fish are enthusiastic grazers, constantly working over leaves, hardscape, and glass. They have a clean silver-gold body with a bold black stripe running from snout to tail, making them genuinely attractive rather than just functional.
Water conditions should sit in the soft-to-moderate range, 6.5 to 7.5 pH with moderate hardness, which conveniently overlaps with most planted tank setups. They prefer some flow and appreciate well-oxygenated water. Temperature anywhere from 24 to 28 Celsius suits them fine.
Diet is where expectations need managing. Juveniles readily devour algae, but as they mature past 8 to 10 centimeters, many individuals start prioritizing sinking pellets, wafers, and any meaty food that drifts by. You can slow this shift by keeping food offerings modest, but it's a known and common outcome. Don't buy one solely as an algae solution and then feed it heavily.
Confusion with lookalike species is rampant. Flying Foxes and Chinese Algae Eaters are frequently sold under the same name, and neither behaves the same way. The true SAE has a solid, unbroken black stripe that extends into the tail fin and no gold stripe above it. Worth double-checking before you buy.
Browse community tank builds with this species to see how aquascapers work around the adult size and behavior shift.
Water Parameters
Temperature
°CpH
GH
dGHKH
dKHSwimming Level
Flow Preference
Keeping multiple Siamese Algae Eater together
Siamese Algae Eater are shoaling fish and need company of their own kind. Keep a group of at least 5. Smaller groups leave them stressed, washed-out in color, and prone to hiding.
Compatibility
They pair well with most community fish including tetras, rasboras, danios, peaceful cichlids like rams or apistogrammas, and virtually any mid-water schooling species. Bottom-dweller overlap with corydoras is generally fine since SAEs spend more time grazing vertical and mid surfaces than competing for the same ground. Avoid housing them with very small shrimp like neocaridina juveniles or dwarf species, as large adults may pick them off opportunistically. Chinese Algae Eaters are a bad pairing since they become aggressive and territorial as adults. In a 200-liter or larger tank, a single SAE fits seamlessly into most community setups.
Commonly kept with
Species this one is most often paired withCommonly tried but avoid
Often paired, but shouldn't beCare Notes
The biggest beginner mistake is buying one expecting a lifelong algae machine. Juveniles deliver, but adults often shift to pellets and ignore algae almost entirely. A second common failure is buying in pairs or trios, which creates a bully-victim dynamic. Go solo or go six-plus. Make sure the tank has a lid because they jump without warning. Avoid confusing them with Flying Foxes at the store, check that the black stripe runs unbroken into the tail and there's no second gold stripe above it before purchasing.
Behavior & Aggression
Siamese Algae Eaters are largely peaceful toward dissimilar species but can get chippy with their own kind, especially in smaller groups of two to four fish where a dominant individual will chase others relentlessly. Aggression also increases at feeding time when sinking foods are involved. They don't nip fins and rarely harass fish outside their own species, but they do establish feeding territories on flat surfaces. Keeping them solo or in a group of six or more tends to diffuse this tension significantly.
Things to Know
- Adults often lose interest in algae and prefer prepared foods
- Can become territorial with own species, keep singly or in groups of 6+
- Commonly mislabeled as Flying Fox or Chinese Algae Eater at stores
- Jumps readily, a tight-fitting lid is essential
- Grows much larger than when purchased, up to 15 cm.
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