Siamese Algae Eater (SAE)

Geographical Origin & Biotope:

*Crossocheilus oblongus* (frequently known by the old name *C. siamensis*) is widely distributed in continental Southeast Asia, including the Mekong river basin and the Chao Phraya basins in Thailand, extending into the Malay Peninsula. They populate clear, shallow rivers and streams that flow quickly over beds of stones, pebbles, and sunken logs—areas extremely rich in algal cover favored by strong sun exposure.

Taxonomy & Morphology:

It is a member of the large Cyprinidae family. The body is streamlined, typical of strong swimmers, and laterally compressed; the back is slightly arched while the belly is flat to rest on stones. The mouth is in an inferior position and is equipped with two pairs of almost invisible barbels (short "whiskers") that act as tactile receptors, and thick fleshy lips designed not to suck but to cut and "rasp" the algae. They reach a respectable size of 15-16 cm (6 inches).

Social Behavior:

It is a group fish. Buying just one will make it visibly uncomfortable; in a small group of 3-5 individuals, they will become very bold. They are not tight schooling fish like Tetras, but they constantly keep an eye on each other. Hierarchical skirmishes exist between SAEs (breakneck chases around the tank) but these never result in actual physical damage.

Coloration & Sexual Dimorphism:

The livery is not flashy but is unmistakably elegant and functional. The base body is a sober silvery-grey scaled on the back and white on the belly. The single distinguishing feature is the single longitudinal black line, sharp and jagged (zigzag) on the margins, which runs from the nose (passing over the eyes) along the entire flank to end not at the base of the tail, but *extending straight through the fork of the transparent caudal fin*. The other fins are strictly colorless. Sexual dimorphism is absent in juveniles; in old specimens, females appear decidedly more massive and rounder in the belly compared to the slender males.

Tank Setup:

The ideal setup is the natural planted aquarium. The layout should feature large broad leaves (Echinodorus, giant Anubias, Water Lilies) or tangled wooden branches on which these fish love to "park" themselves using their pectoral fins as kickstands. Their utility as algae eaters is unquestionable, but there is a catch: they grow up to 14-16 cm (6 inches). Therefore, a school of SAEs requires tanks at least 100-120 cm (3-4 feet) long. A tight-fitting lid is categorically mandatory: these fish, accustomed to the rapids of Asian rivers, are exceptional jumpers and will often launch themselves out of the tank if startled.

Diet & Feeding:

This is the reason they are purchased. Young SAEs (3-6 cm / 1-2 inches) are tireless lawnmowers: they graze continuously on rocks, glass, wood, and plants, strongly preferring the tenacious Black Beard Algae (BBA) and hair algae, which they scrape off using their specialized mouths. They do not damage tender leaves, unlike plecostomus. A crucial warning: as they grow, if overfed with protein-rich dry tropical fish foods (which they quickly learn to steal mid-water), they will become obese and "lazy," stopping their algae-eating because they prefer the easy food. To keep them working, keep the feeding regime sparse and feed the tank in modest quantities, supplementing the SAEs' diet with blanched zucchini and spirulina wafers only when the aquarium is clean of algae.

Water Quality:

Being flowing-water fish, oxygenation is their chemical priority. They thrive in standard tropical waters (24-26°C / 75-79°F) but despise stagnant or turbid tanks; a brisk current and well-filtered water with good surface agitation (promoting gas exchange) will make them robust. They tolerate a wide range of pH (from 6.5 to 7.5) and hardness (GH 5-15), but the water must be kept clean of nitrates, to which they are moderately sensitive.

Compatibility & Tankmates:

The SAE is one of the absolute best community tankmates. It does not bother any other fish, small or large. It will often swim alongside other barbs or rasboras out of pure gregarious instinct. The only note of caution is their explosive vivacity as adults: a 15 cm (6-inch) SAE darting from one side of the tank to the other can stress very slow and delicate fish like Discus. It is excellent with Dwarf Cichlids (Apistogramma, Rams) as it does not eat eggs and grazes peacefully.

Aquarium Breeding:

There are no verified reports of amateur captive breeding. Commercial imports derive from wild catches or huge Asian farms that induce seasonal spawning through hormonal injections, a process impossible to replicate in a living room.

Risks & Diseases:

Physically they are mules, resistant to almost all pathologies if the water is well oxygenated. The greatest risk is, incredibly, misidentification at the time of purchase. In stores, very similar but useless or aggressive fish (like the Flying Fox, *Epalzeorhynchos kalopterus*, or the Chinese Algae Eater, *Gyrinocheilus aymonieri*) are often sold as SAEs. A true SAE is recognized by the horizontal black band that has jagged (zigzag) edges and continues *all the way into* the transparent caudal (tail) fin.