Minute Ricefish (Oryzias minutillus)

Minute Ricefish is one of the smallest freshwater fish species in the world, prized by nano‑aquarium and biotope enthusiasts for its tiny size, gentle behavior, and fascinating ecology.

Taxonomy

• Family: Adrianichthyidae (ricefishes)
• Genus: Oryzias
• Species: Oryzias minutillus

Common Names

• Minute Ricefish
• Dwarf Ricefish
• Mini Ricefish

Distribution

• Native to mainland Southeast Asia
• Recorded from:
  • Thailand
  • Cambodia
  • Vietnam
  • Laos
  • Peninsular Malaysia

Natural Habitat

• Shallow, slow‑moving waters:
  • Rice paddies
  • Flooded fields
  • Swamps
  • Ditches and marshes
• Often found among:
  • Emergent grasses
  • Fine‑leaved aquatic plants
• Environmental conditions:
  • Still or very gentle flow
  • Warm temperatures
  • Soft to moderately hard water
  • Neutral to slightly acidic pH

This species is adapted to ephemeral waters that may dry seasonally.

Size

• Maximum length: ~1.2–1.5 cm (0.5–0.6 in)
• Among the smallest vertebrates regularly maintained in aquariums

Appearance

• Slender, translucent body
• Silvery to pale beige coloration
• Large eyes relative to body size
• Males may show:
  • Slightly longer fins
  • Subtle iridescence during courtship

Color is understated but elegant, especially in planted or blackwater aquariums.

Behavior

• Extremely peaceful
• Active schooling/shoaling fish
• Spends time in the upper and mid‑water levels
• Best kept in groups of 10–20+ due to their minute size

They show fascinating micro‑interactions and spawning behavior when kept in groups.

Diet

In the Wild

• Microscopic aquatic invertebrates
• Zooplankton
• Insect larvae

In Aquariums

Requires very fine foods:

• Infusoria
• Paramecium
• Microworms
• Vinegar eels
• Newly hatched brine shrimp (for adults)
• Powdered fry foods

 Standard flake and pellet foods are usually too large.

Aquarium Care

Tank Size

• As small as 5 gallons, though 10+ gallons is strongly recommended for stability

Water Parameters

• Temperature: 22–28 °C (72–82 °F)
• pH: 6.0–7.5
• Hardness: Soft to moderate
• Very gentle filtration (sponge filter preferred)

Setup Tips

• Dense plants (Java moss, fine stems, floating plants)
• Dark substrate enhances visibility
• Tight lid—tiny fish can jump or get pulled into overflows
• No strong currents

Compatibility

Suitable tankmates:

• None, or other ultra‑small, non‑competitive species
• Best in species‑only tanks

 Avoid:

• Betta
• Gouramis
• Tetras
• Shrimp (even shrimp may prey on fry)
• Any fish larger than ~2 cm

They are easily outcompeted or eaten.

Breeding

• Continuous spawner
• Females carry eggs briefly before depositing them on plants or moss
• Eggs hatch in ~7–10 days
• Fry are extremely tiny and require infusoria immediately

Breeding is possible but considered advanced due to feeding challenges.

Aquarium Trade Notes

• Rare and sporadic availability
• Often imported accidentally with other ricefish
• Popular with:
  • Nano‑tank specialists
  • Biotope aquarists
  • Conservation‑minded hobbyists

Summary

Oryzias minutillus is a remarkable species that rewards patient, detail‑oriented aquarists. While not colorful in the traditional sense, its scale, behavior, and biology make it one of the most fascinating nano fish available.