Licorice Gourami (Parosphromenus deissneri)

Parosphromenus deissneri is a diminutive labyrinth fish (reaching only 3.5–4 cm) native to the blackwater peat swamps, forest streams, and pools of peninsular Malaysia, Singapore, and Sumatra, Indonesia. It belongs to a genus of small, specialized gouramis collectively known as Licorice Gouramis or Licorice Fish — named for the dark, almost black base coloration of many species.

Males display delicate but beautiful coloration: the dark body is accented with horizontal bands or spots of iridescent blue, green, and red that intensify dramatically during courtship and spawning displays. The fins show ornate patterning with metallic blue-green edges. Females are considerably plainer with pale, brownish coloration and less ornate fins.

Licorice Gouramis are bubble nest builders — males construct small nests under floating leaves, overhanging surfaces, or in cave structures where eggs are deposited and guarded by the male. They practice biparental care in some behavioral variants, with males taking primary responsibility.

These fish are extreme specialists of one of the world's most hostile freshwater environments — blackwater peat swamp waters with pH values as low as 3.0–4.5, virtually zero mineral content, and high concentrations of dissolved organic acids. Meeting these water chemistry demands in the aquarium is the primary challenge of keeping this species successfully.

Licorice Gouramis demand authentic blackwater conditions: pH 3.5–6.0, hardness 0–2 dGH (virtually no dissolved minerals), and temperatures 24–28°C. Standard tap water is almost universally unsuitable. Reverse osmosis (RO) water or collected rainwater, supplemented with peat, Indian almond leaves, and botanical material to achieve authentic tannin-rich, ultra-soft conditions is essential.

A small, dedicated blackwater aquarium of 30–60 liters is ideal. Create a dense botanical environment: dark substrate, extensive driftwood, dried leaves (Indian almond, oak), and floating plants to diffuse surface light. Very gentle sponge filtration — these fish inhabit virtually still water. Dim lighting to replicate the deeply shaded forest swamp environment.

Feed exclusively small live or frozen foods: daphnia, baby brine shrimp nauplii, micro worms, copepods, and very small bloodworms. They may refuse dried foods entirely. Feed small amounts 2–3 times daily.

Licorice Gouramis must only be kept with species that tolerate the same extreme blackwater conditions: small Boraras rasboras, small Apistogramma species from similar habitats, and freshwater shrimp adapted to very soft water (Caridina species). Avoid all hard-water species.

Keep in pairs or small groups. Males may display territorial behavior toward each other but rarely cause injury in planted tanks with sufficient cover. This is a specialist species recommended for experienced aquarists committed to providing its specific needs.