Caridina multidentata — Amano Shrimp

Species Overview

Caridina multidentata, commonly known as the Amano Shrimp, Yamato Shrimp, or Algae-Eating Shrimp, is a species of freshwater dwarf shrimp in the family Atyidae. Originally described by the German carcinologist Heinrich Balss in 1914, the species was long misidentified as Caridina japonica before taxonomic revision confirmed its current name. The genus Caridina encompasses over 300 species, many of which are popular in the aquarium trade, but C. multidentata holds a unique position as one of the earliest and most effective biological algae-control agents introduced to the hobby.

Native to the coastal rivers and streams of Japan, Taiwan, and parts of eastern China, Amano Shrimp inhabit slow-moving, densely vegetated waters with moderate current and high oxygen levels. They are amphidromous: adults live in freshwater, but larvae require brackish water to develop, a fact that complicates captive breeding and makes almost all aquarium specimens wild-caught or farmed in brackish conditions. In the wild, they graze on biofilm, algae, and detritus, playing a vital role in nutrient cycling.

In the aquarium hobby, the Amano Shrimp was popularized by Takashi Amano, the legendary aquascaper, who used them in his Nature Aquarium layouts to control filamentous algae without chemicals. Their reputation as superior algae eaters, combined with their peaceful temperament and striking translucent bodies marked by a distinctive lateral row of reddish-brown dashes, makes them a staple in planted tanks and community aquariums worldwide. They are not true fish, but rather decayed crustaceans; however, they are grouped under 'aquarium fish' in trade contexts due to their popularity alongside fish.

Tank Requirements

Minimum tank size: 10 gallons (38 liters) for a small group of 3–5 individuals. A single shrimp can survive in a well-established 5-gallon nano tank, but social groups of at least 3–5 are recommended for natural behavior and reduced stress.

Substrate: Fine, smooth gravel or sand is ideal. Sharp substrates can damage their delicate exoskeleton and antennae. In planted tanks, nutrient-rich aquasoil (e.g., ADA Amazonia) works well, but inert sand or gravel with root tabs is also acceptable. Dark substrates help them feel secure and enhance their coloration.

Decor: Provide ample hiding places and grazing surfaces. Driftwood, smooth rocks, and dense plantings (e.g., Java moss, Anubias, Vallisneria) are essential. Leaves (Indian almond, mulberry) add biofilm and tannins that mimic their natural habitat. Avoid sharp decorations. A cover of floating plants reduces light intensity and stress.

Tank Mates: Amano Shrimp are entirely peaceful and can be kept with small, non-aggressive fish. Ideal tank mates include small tetras (neon, ember), rasboras (harlequin, chili), dwarf corydoras, otocinclus, and snails. Avoid: large cichlids, aggressive barbs, goldfish, and any fish large enough to eat them (e.g., angelfish, bettas, gouramis). Even peaceful fish may nip at shrimp during molting. Provide dense plant cover to allow shrimp to retreat during vulnerable periods.

Water Parameters

Parameter	Optimal Range	Notes
Temperature	70–78 °F (21–26 °C)	Stable; avoid rapid fluctuations above 82 °F
pH	6.5–7.5	Neutral to slightly acidic; stable pH critical
General Hardness (GH)	4–8 dGH	Essential for molting; too soft leads to failed molts
Carbonate Hardness (KH)	2–5 dKH	Buffers pH; too low causes pH swings
Ammonia (NH₃/NH₄⁺)	0 ppm	Highly toxic; any detectable level is harmful
Nitrite (NO₂⁻)	0 ppm	Blocks oxygen uptake; must be zero
Nitrate (NO₃⁻)	<20 ppm	<10 ppm ideal; above 40 ppm stresses shrimp

Key fact: Amano Shrimp are sensitive to copper and heavy metals. Use only shrimp-safe water conditioners. Sudden parameter shifts (especially pH >0.5 change or temperature >3°F swing) can trigger premature molting, often fatal.

Filtration and Lighting

Filter type: Sponge filters or hang-on-back (HOB) filters with a pre-filter sponge are best. Strongly avoid canister filters or powerheads with uncovered intakes—shrimp and their larvae can be sucked in and killed. Sponge filters provide gentle flow and excellent biological filtration while serving as a grazing surface for biofilm.

Flow preference: Moderate to low flow. Amano Shrimp are not strong swimmers; high current stresses them and prevents efficient grazing. Position filter output against a wall or use a spray bar to diffuse flow. Stagnant zones are acceptable as long as oxygen exchange is adequate (surface agitation).

Lighting: Moderate lighting (0.5–1 watt per liter LED) is sufficient. They are not light-dependent themselves, but bright light promotes algae growth, which they eat. However, intense light without algae control can cause cyanobacteria blooms. A 6–8 hour photoperiod with a siesta (mid-day break) mimics natural conditions and reduces algae spikes. No special spectrum needed; standard daylight LEDs work.

Diet and Nutrition

Staple food: High-quality sinking shrimp pellets or algae wafers (e.g., Hikari Crab Cuisine, Repashy Soilent Green). These provide balanced protein, fiber, and minerals. Avoid foods with high copper sulfate (check labels).

Treats: Blanched vegetables (zucchini, spinach, cucumber, kale—boiled 2–3 minutes until soft), spirulina powder, frozen daphnia, brine shrimp (rinsed), and mulberry leaves. Offer treats 1–2 times per week. Uneaten vegetables must be removed after 24 hours to prevent ammonia spikes.

Feeding frequency: Once daily, with one fasting day per week. In well-planted tanks with biofilm, feeding every other day is sufficient. They will constantly graze on algae and detritus, but supplemental feeding prevents malnutrition.

Portion rule: Feed an amount they can consume within 2–3 hours. For a group of 5 shrimp, a quarter of an algae wafer or a pinch of pellets is enough. Overfeeding leads to water quality degradation and planaria outbreaks.

Supplements

Calcium is the most critical supplement for Amano Shrimp. It is essential for proper exoskeleton formation and successful molting. Provide via:

• Cuttlebone (boiled to remove salt, then broken into small pieces and placed in tank)
• Shrimp-specific mineral blocks (e.g., Shrimp Mineral, Bacter AE)
• Calcium-rich foods like blanched spinach or kale

Iodine is also vital for molting. Most quality shrimp foods contain trace iodine, but in soft water (<3 dGH), iodine deficiency can occur. Use a shrimp-specific supplement (e.g., Seachem Iodine) at 1 drop per 10 gallons weekly, but only if GH is low. Never overdose—iodine is toxic at high levels.

Biofilm enhancers like Bacter AE (a probiotic powder that promotes biofilm growth) can be added weekly to provide continuous grazing. This mimics their natural diet and reduces reliance on prepared foods.

Common Health Issues

1. Molting Problems (Dyscdysis)
   Symptoms: Shrimp trapped in old exoskeleton, white band around the body ("ring of death"), lethargy, lying on side.
   Cause: Low calcium or iodine, rapid water parameter changes, soft water (GH <3 dGH).
   Treatment: Gradually raise GH to 4–6 dGH using shrimp-specific remineralizer. Add cuttlebone or calcium block. Avoid water changes during molting. Isolate affected shrimp in a container with stable parameters.
2. Bacterial Infections (e.g., Pseudomonas)
   Symptoms: Opaque or milky muscles, red spots on exoskeleton, erratic swimming, sudden death.
   Cause: Poor water quality, injury, introduction of infected shrimp.
   Treatment: Improve water quality (50% water change daily for 3 days). Add Indian almond leaves (tannins have mild antibacterial properties). Remove visibly infected shrimp to a hospital tank. Use shrimp-safe antibiotics (e.g., Seachem Kanaplex) only as last resort—most antibiotics are toxic to shrimp.
3. Fungal Infections (e.g., Saprolegnia)
   Symptoms: White cottony growth on exoskeleton, especially around gills or wounds, lethargy.
   Cause: Injury, poor water quality, low temperatures.
   Treatment: Salt bath (1 teaspoon aquarium salt per 2 liters of tank water, 30-second dip) for mild cases. Improve water quality. Remove dead shrimp immediately. Preventive: maintain stable temperature above 70°F.
4. Parasitic Infestations (e.g., Scutariella japonica)
   Symptoms: White, worm-like parasites on the rostrum (nose), antennae, or legs. Shrimp may scratch against decor.
   Cause: Introduced via wild-caught shrimp or contaminated plants.
   Treatment: Salt dip (same as fungal). For heavy infestations, use a shrimp-safe antiparasitic like Seachem ParaGuard (half dose). Quarantine new shrimp for 4 weeks.
5. Copper Poisoning
   Symptoms: Lethargy, loss of appetite, paralysis, rapid death within hours.
   Cause: Copper in tap water, fish medications, or fertilizers.
   Treatment: Immediate large water change (90%) with dechlorinated, copper-free water. Use activated carbon in filter. Add Seachem CupriSorb if available. Prevention: test tap water for copper; use shrimp-safe fertilizers (e.g., NilocG ThriveS).

Beginner Mistakes

• Adding shrimp to an uncycled tank. Amano Shrimp are extremely sensitive to ammonia and nitrite. Always cycle the tank fully (4–6 weeks) before introduction. Use a liquid test kit; test strips are unreliable.
• Large, sudden water changes. Changing more than 30% of water at once, or using water with different temperature/pH, triggers premature molting and death. Always drip-acclimate new water over 1–2 hours.
• Keeping with aggressive or large fish. Even semi-aggressive species like dwarf gouramis or cherry barbs will nip at shrimp, especially during molting when they are vulnerable. Research tank mates thoroughly.
• Overfeeding. Leftover food decays, spiking ammonia and causing bacterial blooms. This is the #1 cause of shrimp deaths in established tanks. Feed sparingly and remove uneaten food within 2 hours.

FAQ

Can Amano Shrimp breed in freshwater?

No, not in typical aquarium conditions. The larvae require brackish water (salinity around 1.015–1.020 specific gravity) to develop through their planktonic stages. In freshwater, larvae die within days. Some advanced hobbyists have successfully raised them by transferring larvae to a separate brackish tank, but it is challenging and rarely done.

How many Amano Shrimp should I keep together?

A group of at least 3–5 is recommended. They are social and feel more secure in numbers. In a 10-gallon tank, 5–8 is ideal. Overcrowding (>10 in a 10-gallon) can cause stress and water quality issues. They do not breed in freshwater, so population control is not a concern.

Why is my Amano Shrimp turning white or pink?

Mild color changes are normal—they become paler when stressed or after molting. However, a persistent white or milky appearance often indicates a bacterial infection or molt failure. Check water parameters (especially GH and KH) and ensure no copper in the water. Pinkish coloration can be a sign of stress from high temperature or poor water quality. If accompanied by lethargy, quarantine and treat.

Do Amano Shrimp eat hair algae?

Yes, they are one of the best biological controls for filamentous algae including hair algae, thread algae, and staghorn algae. They also consume green spot algae and diatoms. However, they are less effective on black beard algae (BBA) and cyanobacteria. For BBA, manual removal and improving CO₂ levels are more effective.

Can I keep Amano Shrimp with Cherry Shrimp (Neocaridina davidi)?

Yes, they are compatible. They occupy different ecological niches (Amano are larger and more active grazers) and do not hybridize. However, ensure the tank is large enough (15+ gallons) to avoid competition for food. Cherry shrimp may be outcompeted for algae wafers; supplement with sinking pellets in multiple locations.

References