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Moscow Blue Guppy

Poecilia reticulata var. Moscow Blue

The Moscow Blue is the aristocracy of Guppies. Males are dressed in a velvety cobalt blue from head to tail, without any spots. Unfortunately, decades of inbreeding to fix this perfect color have made them genetically deformed. As they grow, their fragile spine collapses under the titanic weight of their tail. In addition, females are true reproductive machines: capable of storing sperm from a single mating for months, they will give birth to 40-50 fry every month, sparking a population explosion that will devastate your aquarium.

Taxonomy
Class:Actinopteri
Order:Cyprinodontiformes
Family:Poeciliidae
Genus:Poecilia
Species:Poecilia reticulata var. Moscow Blue

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Water Temperature

22 - 28 °C

pH Value

7 - 8.5

Water type

Freshwater

Tank level

All levels

Adult size

5 cm

Minimum tank volume

>= 40 L

Minimum group

>= 4

GH

10 - 25 dGH

KH

5 - 12 dKH

TDS

200 - 495 ppm

Conductivity

313 - 773 uS/cm

Species description

Geographical Origin and Habitat: Highly selected strain born in Moscow (Russia) during the Cold War, developed by isolated aquarists trying to fix unique color mutations starting from guppies imported decades earlier.
Taxonomy and Morphology: Moscow Blue Guppy (Poecilia reticulata). Elite poeciliid. The "Moscow" characteristic is the extension of the pigment over the entire body, including the head (a very rare trait in guppies, where color usually stops mid-trunk).
Social Behavior: Exuberant but heavy. The Moscow Blue male is often weighed down by immense dorsal fins (which fall like a cloak) and caudal fins. It swims incessantly looking for mating, tiring very quickly in case of strong currents.
Coloration and Sexual Dimorphism: Ink Blue Velvet. The male is a solid block of deep midnight blue color, almost black in some lights, metallic and sparkling under white LEDs. The female is large (6 cm / 2.4 inches), gray/silver with transparent or slightly gray/blue edged fins.

Care, breeding and tankmates

Aquarium Setup: Sweet and calm aquarium (60 cm / 24 inches). Being a prized strain, the ideal tank is a clean Iwagumi-style layout or densely planted (Dutch) with practically still water so as not to exhaust the males. Always insert floating plants to shield aggressive light.
Diet and Feeding: Exhibition omnivore. To keep the deep blue pigment (without letting it turn to red or dull yellow), administer specific feeds rich in Astaxanthin and spirulina, supplementing with live or frozen mosquito larvae (bloodworms).
Water Quality: Like all Russian and Asian guppies, it is a high-level inbred. Intolerant to soft and acidic water (the pH must be strictly above 7.2) and to nitrate accumulation. Requires regular partial changes and a GH 12-20.
Compatibility and Cohabitation: Excellent prey. Their dark color and very slow swimming make them the favorite target of aggressive fish. Keep only in monospecific tanks or pair exclusively with peaceful Corydoras or Otocinclus.
Aquarium Breeding: The Breeder's Challenge. Although they breed easily like all guppies (ovoviviparous, 30 fry a month), keeping the "Blue Moscow" line pure is very difficult. If breeders are not obsessively selected, discarding those with red or yellow spots, the strain will degrade in a few generations.
Risks and Diseases: The mutant gene and the Swim Bladder. Many high-quality Moscows develop a genetic defect in the swim bladder as they age, ending up swimming "upside down" or sinking. If you notice a zig-zag gait on the bottom, the fish is incurable.

Geographic Origin and Distribution

Highly selected strain born in Moscow (Russia) during the Cold War, developed by isolated aquarists trying to fix unique color mutations starting from guppies imported decades earlier.

Origin

Selective breeding and cultivars
Varietà da Selezione / Cultivar

Fish profile

Temperament
Peaceful
They possess a peaceful, active, and generally social temperament. They are constantly in motion, exploring their environment and interacting with conspecifics. While males may display and occasionally spar for dominance or mating rights, serious injuries are rare. Their inquisitive nature makes them very engaging and entertaining to observe. A well-structured environment further encourages their natural, peaceful behaviors to shine through.
Diet
Omnivore
They are omnivorous and thrive on a varied diet to maintain optimal health. High-quality flake foods or micro-pellets should form the staple of their daily feeding. Supplementing their diet with live or frozen foods like daphnia, brine shrimp, and bloodworms is highly recommended. Including vegetable matter such as spirulina will also benefit their digestive system. A balanced and varied diet enhances their immune system and brings out their best colors.
Sex ratio
Specific M:F ratio
A recommended sex ratio is keeping at least two or three females for every male. This ratio helps to disperse the male's constant harassment and mating attempts among several females. Keeping a balanced ratio significantly reduces the stress experienced by the females. If too many males are present, the constant pursuit can lead to exhaustion and compromised immune systems in females. In larger setups, this ratio can naturally fluctuate but should generally be maintained to ensure harmony.
Feeding frequency
Twice daily
It is optimal to feed them small amounts multiple times a day, ideally two to three times. This frequent feeding mimics their natural foraging behavior in the wild. Ensure that only an amount they can consume within a couple of minutes is provided to prevent overfeeding. Leftover food can rapidly degrade water quality and lead to health issues. Adjusting the feeding frequency based on the fish's activity levels and age is a good practice.
Bioload
They produce a relatively low bioload compared to larger aquarium fish. This makes them suitable for smaller aquariums if maintained properly. However, their prolific breeding can quickly increase the total bioload of the tank. Regular water changes and good filtration are essential to maintain water quality. Monitoring nitrate levels is important to ensure the bioload is being effectively managed.
Flow
Stagnant
They typically prefer gentle to moderate water movement within the aquarium. Strong currents can be exhausting for them, especially for males with large, flowing fins. A sponge filter or a well-baffled hang-on-back filter often provides the ideal flow rate. Providing areas of both slight movement and still water allows them to rest when needed. An appropriate flow rate also ensures adequate oxygenation without causing undue stress to the fish.
Reproduction
Oviparous
As livebearers, they are exceptionally easy to breed and will often multiply without any special intervention. Females can store sperm for several months, resulting in multiple drops of fry from a single mating. The gestation period typically lasts around three to four weeks, depending on water temperature. To ensure the survival of the fry, providing plenty of hiding spaces like dense vegetation or breeding grass is essential. Adults may predate on their own young, so a separate breeding tank might be necessary for maximum yield.
Compatibility & tankmates
Harem only
These fish are generally peaceful and make excellent additions to community aquariums. They can be kept with other small, non-aggressive species like tetras and corydoras. It is best to avoid keeping them with known fin-nippers such as tiger barbs. Aggressive or much larger fish might view them as food and should be avoided. A harmonious community tank ensures their long-term health and vibrant coloration.
Tank level
All levels
They are extremely active and will utilize all levels of the aquarium. However, they show a strong preference for the middle and upper levels of the water column. They are frequently seen swimming near the surface, especially during feeding times. Providing open swimming space in the upper regions alongside some floating cover makes them feel secure. Their presence in the upper layers adds vibrant movement and life to the top portion of the tank.

Window to the official scientific data of the species

Data synced on: 06/15/2026

Scientific Parameters & Models

Trophic level
3.2 ± 0.4 se
Resilience
High (less than 15 months)
Generation time
0.6 years
Phylogenetic uniqueness (PD50)
0.5
Bayesian Length-Weight
a = 0.01288, b = 3.14
VulnerabilityLow to moderate vulnerability (33 / 100)

Image gallery

Licensed images linked to the species or, when marked, to the closest representative taxon.

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Last updated: 06/30/2026
Moscow Blue Guppy (Poecilia reticulata var. Moscow Blue) Care Guide & Tank Setup | Atlarium