Siamese Algae Eater (Crossocheilus oblongus)

Taxonomy and Classification

Siamese Algae Eater, scientifically known as Crossocheilus oblongus, belongs to the family Cyprinidae, subfamily Labeoninae, within the order Cypriniformes. The species was described by Valenciennes in 1842 from specimens collected in Southeast Asia. For decades, the aquarium trade used the name Crossocheilus siamensis, but modern taxonomic revision has established C. oblongus as the correct scientific name for the true Siamese Algae Eater. Additional species including C. langei and C. atrilimes have been sold interchangeably under the same common name, causing widespread confusion.

The common name derives from the species' native range in Siam, the former name for Thailand, and its remarkable appetite for algae. It is also known as the SAE, True SAE, or BBA Destroyer in the planted aquarium community. The genus Crossocheilus contains multiple similar-looking species, which contributes to the persistent misidentification problem in the aquarium trade.

Natural Distribution and Habitat

The Siamese Algae Eater is native to Southeast Asia, specifically the Chao Phraya and Mekong river basins, as well as the Malay Peninsula. Its range extends through Thailand, Malaysia, and possibly into Indonesia, specifically Sumatra, Borneo, and Myanmar. The type species was collected near Palembang, Sumatra.

Their natural habitat consists of flowing streams and rivers with substrates of sand, gravel, and boulders. These waters are clear, swift-moving, and well-oxygenated, with dense plant life along the margins. The fish spend approximately half their time hiding in shelters formed by rocks, plants, and submerged logs, and the other half scouring surfaces for food. They inhabit waters that are slightly acidic to neutral, soft to moderately hard, and well-oxygenated with moderate to strong current.

Physical Characteristics

Adult Siamese Algae Eaters reach a maximum length of 6 inches (15.2 cm), though many aquarium specimens remain closer to 4 to 5 inches (10 to 12.7 cm). The body is elongated, slender, and torpedo-shaped, adapted for fast, darting swimming in current. The base coloration is olive-brown to golden, with a bold, black horizontal stripe running from the tip of the snout to the end of the tail fin. This stripe extends into the caudal fin, which is the primary diagnostic feature distinguishing true SAEs from impostors. The stripe has ragged, uneven edges rather than smooth, clean lines.

The fish possesses a single pair of small, forward-pointing barbels on the upper lip. All fins are clear and transparent without colored markings. A key anatomical feature is the underdeveloped swim bladder, which causes the fish to rest on the substrate using its pectoral and pelvic fins, with the body angled slightly upward. Sexual dimorphism is subtle; females have a broader, fuller body profile, while males are more slender and streamlined. Juveniles sold in shops are typically 1 to 2 inches (2.5 to 5 cm) and grow to full size within 18 to 24 months under optimal conditions.

Conservation and Trade Considerations

The species is listed as Not Evaluated by the IUCN. Virtually all specimens in the aquarium trade are wild-caught or farm-raised in Southeast Asia. The species has not established invasive populations outside its native range. The primary concern for aquarists is not conservation status but correct identification, as mislabeled specimens are the norm rather than the exception in many retail outlets.

Aquarium Requirements

Siamese Algae Eaters demand more space than their small juvenile size suggests. A single individual requires a minimum 30 gallon (113 liter) tank with a footprint of at least 36 inches by 12 inches (90 cm by 30 cm). For a group of 5 or more, provide 55 gallons (208 liters) minimum with a length of 48 inches (120 cm). These are powerful, fast swimmers that dart from one end of the tank to the other instantly. Cramped quarters cause stress, reduced algae-eating behavior, and increased aggression toward tank mates.

Filtration and Water Flow

Moderate to strong water flow is essential to replicate their natural riverine habitat. Use a canister filter with a spray bar or lily pipe, or a hang-on-back filter rated for at least 6 to 8 times the tank volume per hour. Good surface agitation increases dissolved oxygen, which active fish like SAEs require. Add a sponge filter for supplemental biological filtration. Avoid stagnant water; these fish evolved in swift currents and become lethargic in still conditions.

Substrate and Hardscape

Use smooth sand or fine rounded gravel as substrate. The fish constantly graze the bottom and rest on the substrate; sharp edges injure their delicate barbels and mouth tissues. Provide driftwood, smooth rocks, and caves for hiding. The fish appreciate having ample cover along the tank perimeter with open swimming lanes in the center. Bogwood and driftwood not only provide shelter but also encourage beneficial biofilm growth that supplements their diet.

Plant Decor

Siamese Algae Eaters thrive in heavily planted tanks. Use dense plant borders along the back and sides with open swimming lanes in the front. Suitable plants include Cryptocoryne, Java Fern, Anubias, Vallisneria, and Amazon Sword. Floating plants such as Amazon Frogbit or Salvinia diffuse overhead light and create shaded retreats. The fish generally do not eat healthy aquatic plants, though they may nibble on delicate mosses or damaged leaves. Robust lighting promotes algae growth on hardscape and glass, which serves as their primary food source.

The Mandatory Lid

A tight-fitting lid is absolutely mandatory. Siamese Algae Eaters are notorious jumpers. Their fast, darting behavior can launch them out of open-top tanks or through small gaps in hoods. Use a glass canopy with all gaps sealed. Check the seal regularly, as filter vibrations can shift covers over time.

Water Parameter Stability

While Siamese Algae Eaters tolerate a broad parameter range, stability is paramount. Sudden pH swings or temperature shocks above 3 degrees Fahrenheit induce acute stress and suppress the immune system. Perform weekly water changes of 25 percent to maintain nitrates below 20 ppm. They prefer slightly cooler water; sustained temperatures above 82 degrees Fahrenheit (28 degrees Celsius) cause lethargy and reduced oxygen tolerance. In warm climates, use cooling fans or chillers during summer months.

Dietary Requirements

Siamese Algae Eaters are omnivores with a strong herbivorous preference. In the wild, they graze on aufwuchs, a complex biofilm of algae, diatoms, bacteria, and microscopic invertebrates coating submerged rocks and plant surfaces. Their most celebrated dietary trait is the consumption of black beard algae (Audouinella or Rhodochorton), a stubborn red algae that forms dark tufts on equipment, hardscape, and slow-growing plant leaves. BBA is the algae that most other algae eaters, including bristlenose plecos, otocinclus, and Amano shrimp, will not touch.

Staple Foods

Algae and biofilm should constitute the majority of their diet in a well-lit, mature aquarium. Supplement with algae wafers, spirulina tabs, and blanched vegetables including zucchini, cucumber, spinach, peas, and lettuce. Feed vegetables daily if algae growth is insufficient. Blanched vegetables provide essential fiber without the protein overload of commercial pellets.

Supplemental Foods

Offer frozen bloodworms, brine shrimp, or daphnia twice weekly only. These protein sources enhance coloration and provide variety, but excessive protein causes severe internal issues and suppresses algae-eating behavior. Live foods such as mosquito larvae and daphnia stimulate natural hunting behavior. The fish will also consume detritus and leftover food from the substrate, functioning as effective scavengers.

The Critical Feeding Rule

If your primary goal is algae control, you must limit commercial food. Offer sinking pellets or wafers only 2 to 3 times per week. A hungry Siamese Algae Eater is a working algae eater. If well-fed with tasty commercial foods, they quickly lose interest in algae and become lazy grazers. This is the most common reason aquarists are disappointed with their SAE's algae-eating performance. Do not overfeed community tank mates either, as SAEs will scavenge leftovers and ignore algae.

Prohibited Foods

Never feed beef heart, pork, or other mammalian proteins. Cyprinids lack the digestive enzymes to process mammalian fats, leading to fatty liver degeneration. Avoid dried foods past their expiration date, as vitamin degradation causes deficiency disorders within weeks. Do not rely exclusively on flake foods, which disintegrate before reaching the bottom where SAEs feed.

Captive Breeding Overview

Breeding Siamese Algae Eaters in home aquariums is considered extremely difficult and has rarely been accomplished without hormonal stimulation. Commercial production relies almost exclusively on hormone-induced spawning in farms. The primary obstacles are the difficulty of sexing the fish, their need for very specific environmental triggers, and their egg-scattering behavior in open water.

Sexual Dimorphism

Distinguishing male from female Siamese Algae Eaters is challenging. Females have a broader, fuller body profile, particularly when viewed from above, while males tend to be more slender and streamlined. During breeding condition, females may appear noticeably plumper as they fill with eggs. There are no reliable color differences between the sexes. The subtle nature of these differences makes deliberate pair formation nearly impossible for hobbyists.

Spawning Triggers

In the wild, Siamese Algae Eaters breed during the rainy season when water levels rise, temperatures drop slightly, and fresh rainwater inundates the streams. To simulate these conditions in captivity, some breeders have attempted lowering the temperature to 68 degrees Fahrenheit (20 degrees Celsius), performing large 50 percent water changes with cool RO water over 6 hours, and increasing water flow velocity. However, success rates remain extremely low without hormonal assistance.

Spawning Behavior and Egg Care

They are egg scatterers that release adhesive eggs over fine-leaf plants or gravel substrate. A mature female may release 1,000 to 3,000 eggs during a single spawning event. The parents exhibit no parental care and will consume the eggs if not removed. Eggs hatch in 24 to 36 hours at 75 degrees Fahrenheit (24 degrees Celsius). The fry are extremely small and require green water, infusoria, or commercially available liquid fry food for the first 5 days. After 7 to 10 days, they can transition to baby brine shrimp nauplii.

Fry Rearing

Grow-out tanks must be at least 20 gallons (75 liters) with gentle sponge filtration and dim lighting. Perform small daily water changes of 10 percent to maintain water quality without shocking the delicate fry. The fry grow slowly initially and require constant access to algae-covered surfaces or green water. Due to the extreme difficulty of breeding this species in captivity, hobbyists are strongly advised to purchase commercially bred or wild-caught specimens rather than attempting home breeding.

Expert Tips for Long-Term Success

Train Them in Quarantine

The single most effective technique for ensuring your Siamese Algae Eater eats black beard algae is to train it during quarantine. Place BBA-covered decor, rocks, or plant leaves in the quarantine tank and withhold all commercial food for the first 5 to 7 days. The hungry fish will quickly develop a taste for BBA. Once established, this feeding behavior persists when the fish is moved to the display tank. Many aquarists fail because they add the SAE directly to a well-fed community tank, where it immediately learns to scavenge fish food instead of grazing algae.

Verify Before You Buy

Misidentification is the norm, not the exception, in the aquarium trade. Before purchasing, insist on examining the fish closely. The true SAE's black stripe must extend into the tail fin and have ragged edges. The fins must be completely clear. If the shop cannot guarantee the species, do not buy. Purchasing a Flying Fox or False SAE results in a fish that not only fails to control BBA but may become aggressive toward your true SAE.

Juveniles Work Best

Young SAEs between 1.5 and 2.5 inches (3.8 to 6.5 cm) are the most effective algae grazers. They have high metabolisms, small mouths that can access tight spaces, and a strong instinct to graze constantly. As they mature, their algae-eating efficiency declines. For ongoing BBA control in a mature tank, consider rotating in younger specimens every 12 to 18 months while rehoming adults that have lost interest in algae.

Address the Root Cause

Siamese Algae Eaters are a biological control tool, not a cure. Black beard algae thrives when CO2 levels fluctuate or water circulation is poor. Use SAEs as part of a broader strategy that includes stable CO2 injection, good flow patterns, proper lighting duration, and regular water changes. If the underlying cause is not corrected, BBA will return regardless of how many SAEs you add.

Feeding Discipline

The most common mistake SAE keepers make is overfeeding the tank. When community tank mates receive generous portions of flakes, pellets, and frozen foods, the SAE abandons algae grazing in favor of easy calories. Feed the tank sparingly. Target-feed individual species with pipettes or feeding rings to ensure the SAE does not scavenge excessive leftovers. Remember the golden rule: a hungry SAE is a working SAE.

Group Size Matters

If you choose to keep multiple SAEs, maintain a group of 5 or more, or keep a single individual. Groups of 2 to 4 often develop bullying hierarchies where dominant fish chase subordinates relentlessly. In a group of 5 or more, the aggression is distributed across the group and rarely results in injury. Inadequate space exacerbates this problem; a 55 gallon (208 liter) tank is the minimum for any group attempt.