Spiny pleco - Pseudolithoxus anthrax

Scientific name: Pseudolithoxus anthrax

Common name: Spiny pleco

Family: Loricariidae

Usual size in fish tanks: 12 - 15 cm (4.72 - 5.91 inch)

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Recommended pH range: 6.5 - 7.7

Recommended water hardness: 6 - 18°N (107.14 - 321.43ppm)

0°C 32°F30°C 86°F

Recommended temperature range: 22 - 28 °C (71.6 - 82.4°F)

The way how these fish reproduce: Spawning

Where the species comes from: South America

Temperament to its own species: peaceful to females

Temperament toward other fish species: peaceful

Usual place in the tank: Bottom levels

Short description

Pseudolithoxus anthrax (hobby: sometimes “Spiny Monster” pleco; L-number commonly associated in the trade) is a small, spiny, rheophilic loricariid from fast, rocky waters of the Orinoco system. Built for current, it clings to stones and grazes aufwuchs (biofilm) and tiny invertebrates. Stunning high-contrast spotting, heavy odontodes (spines), and a compact 12–15 cm adult size make it a prized but oxygen-demanding specialist.

Origin

South America – tributaries of the Orinoco (Venezuela/Colombia), especially clear, fast, rocky stretches with high dissolved oxygen and minimal tannins. Most habitats feature boulder fields, bedrock shelves, and coarse gravel with scant wood.

Food and feeding

Despite the “algae eater” stereotype, this species is best described as an aufwuchs grazer / micro-carnivore. Offer a varied mix: high-quality sinking carnivore wafers/granules, mysis, chopped shrimp, blackworms, bloodworms, cyclops, and finely chopped mussel/krill. Supplement with some green matter (spirulina wafers, blanched zucchini) but do not rely on vegetables alone. Feed modest portions in the evening; maintain excellent cleanliness to protect gills and barbels.

Sexing

Mature males develop more extensive odontodes (spines) on the cheeks and along the pectoral fin rays; females are typically rounder in the belly when gravid.

Breeding

Rare in home aquaria. Presumed cave spawner (as in many hypostomines): eggs deposited in tight crevices/tubes with the male guarding until hatch. If attempted, provide multiple narrow caves, intense aeration, and ultra-stable water.

Lifespan

Commonly 8–10 years with strong oxygenation and pristine water; stress and low O₂ shorten longevity.

Behavior & compatibility

Generally peaceful toward dissimilar species but can become territorial with conspecifics, especially adult males competing for caves. Best kept singly or as a carefully structured group in a large tank with surplus hides. Avoid boisterous tankmates that dominate food or dislike strong current.

Tank requirements

Tank size: 200 L for a single specimen; substantially larger for multiple adults.
Hardscape: rock piles, slate stacks, and narrow caves; wood is optional and not essential for digestion.
Flow & oxygen: high turnover with additional powerheads; vigorous surface agitation; consider air stones 24/7.
Water: pH 6.5–7.7 (slightly acidic to neutral), soft to moderately hard; temperature 22–28 °C (keep O₂ high at warmer temps).
Filtration: oversized bio-mechanical filtration; low nitrate; frequent small water changes; immaculate substrate.
Lighting: moderate to dim; provide shaded retreats to minimize stress.

Care notes

Acclimate slowly. This species is sensitive to sudden chemistry shifts, low oxygen, and lingering organics. Provide more caves than fish to diffuse aggression, and place food directly where they graze so midwater fish don’t outcompete them.