A highly adaptable, sub-tropical livebearer native to South America. Known for its hardiness, it thrives in unheated aquariums and can tolerate mildly brackish water. Unlike many common livebearers, they are voracious algae grazers and may damage soft-leaved plants. Males relentlessly pursue females to mate, so keeping a ratio of at least 2-3 females per male is strongly advised.
Dusky Millions Fish At a Glance
Dusky Millions Fish Tank Requirements
Will Dusky Millions Fish fit in your tank?
Care guides tell you what Dusky Millions Fish needs, the next question is whether your tank can safely provide it. Test Dusky Millions Fish against your tank size, maintenance needs, and the fish you already keep before you buy.
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Dusky Millions Fish Water Parameters
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Dusky Millions Fish Temperament & Compatibility
Dusky Millions Fish Varieties
Each variety inherits the species defaults above. Only differences are highlighted.
Female
Females are much larger and plumper than males. Due to the constant mating attempts from males, a healthy shoal should be heavily female-biased to spread out the harassment.
Same care requirements as the base species
Also known as: Standard, Wild Type
Male
Noticeably smaller than females and featuring a modified anal fin (gonopodium) for reproduction. Males are incredibly active and focused almost entirely on mating.
Differs in 1 trait from base species
Also known as: Gonopodium
Leopard / Spotted Morph
Highly popular melanistic (speckled) or golden strains selectively bred for the aquarium trade (often erroneously sold as P. c. reticulatus). Husbandry and extreme size dimorphism between sexes remain identical to the wild type.
Same care requirements as the base species
Also known as: Reticulatus, Auratus, Dalmatian
Dusky Millions Fish Care Guide Summary
The Dusky Millions Fish, scientifically known as Phalloceros caudimaculatus, belongs to the Livebearers family group. Adults reach a maximum size of approximately 6 cm and have a fusiform body shape with a fast growth rate. Classified as peaceful, this species primarily occupies the surface and mid-level zones of the aquarium and produces a high level of biological waste.
To thrive, the Dusky Millions Fish requires a brackish tolerant aquarium with a minimum volume of 40 litres and a tank length of at least 45 cm. Water temperature should be maintained between 16°C and 24°C, with a pH range of 7–8 and a general hardness of 8–20 dGH. A low water flow is preferred.
Due to its specialist needs, the Dusky Millions Fish is best suited for fishkeepers who can provide a carefully planned setup. This species is available in 3 varieties: Female, Male, and Leopard / Spotted Morph. Each may differ slightly in size, temperament, or care needs, so it is worth checking the specific requirements of the variety you plan to keep.
Dusky Millions Fish Habitat Setup
When setting up an aquarium for the Dusky Millions Fish, a low water flow best suits their natural preferences. Because this species occupies the surface and mid-level zones, the aquarium layout should prioritise adequate surface area with floating cover to make them feel secure near the waterline and open swimming space in the centre of the tank for free movement. Useful additions include an established tank with natural algae growth, as they depend on it as a primary food source, dense planting to provide cover, break sightlines, and reduce stress, and floating plants to diffuse overhead light and create shaded areas. Keepers should note that live planted layouts may be difficult to maintain, as this species tends to uproot or consume vegetation.
Dusky Millions Fish Compatibility Notes
Classified as peaceful, the Dusky Millions Fish is a social species that requires the company of its own kind to thrive. When choosing tankmates, avoid housing with slow-moving or long-finned species that may become targets for fin nipping and their energetic swimming style may stress more sedentary or timid species. Selecting tankmates that favour different water layers from the surface and mid-level zones can help reduce competition and territorial overlap.
Dusky Millions Fish Recommended Tank Sizes
Standard aquarium sizes that meet the minimum volume and length requirements for Dusky Millions Fish.
15 Gallon Standard
20 Gallon High
20 Gallon Long
29 Gallon Standard
30 Gallon Breeder
36 Gallon Bowfront
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Frequently Asked Questions About Dusky Millions Fish
How big does Dusky Millions Fish get?
Dusky Millions Fish (Phalloceros caudimaculatus) typically reaches a maximum adult size of approximately 6 cm. They have a fusiform body shape and a fast growth rate.
What tank size does Dusky Millions Fish need?
A minimum aquarium volume of 40 litres and a tank length of at least 45 cm are recommended for Dusky Millions Fish. This ensures enough swimming space and helps maintain stable water conditions.
What water parameters does Dusky Millions Fish need?
Dusky Millions Fish thrives in brackish tolerant conditions with a temperature range of 16–24°C, a pH between 7 and 8, and a general hardness of 8–20 dGH. A low water flow is preferred.
Is Dusky Millions Fish peaceful or aggressive?
Dusky Millions Fish is classified as peaceful with an aggression score of 2 out of 10. They are generally well-suited to peaceful community tanks.
Can Dusky Millions Fish live alone?
No, Dusky Millions Fish should be kept in groups of at least 5 to reduce stress and encourage natural behaviour.
Does Dusky Millions Fish have any special tank requirements?
Yes. Dusky Millions Fish benefits from plants - densely covered, plants - floating, and established algae (otocinclus) in the aquarium. These features help replicate their natural habitat and promote overall health and well-being.
Top Tank Mates for Dusky Millions Fish
These fish are strong compatibility matches for Dusky Millions Fish based on water preferences, temperament, adult size, and tank behavior.
Dainty Cory (Salt and Pepper Cory)
Corydoras habrosus
Ideal Tank MatesEmerald Green Cory
Corydoras splendens
Ideal Tank MatesGolden Bristlenose Pleco
Ancistrus sp. L144
Ideal Tank MatesAgassiz Cory
Corydoras agassizii
Ideal Tank MatesBlack Corydoras
Corydoras schultzei
Ideal Tank MatesBandit Cory
Corydoras metae
Ideal Tank MatesPlants That Suit Dusky Millions Fish
These plants pair well with Dusky Millions Fish based on shared water preferences, layout fit, and how likely they are to hold up in the same aquarium.
Asian Watergrass
Hygroryza aristata
Asian Watermoss
Salvinia cucullata
Floating Fern
Salvinia natans
Giant Salvinia
Salvinia molesta
Water Cabbage
Pistia stratiotes
Water Hyacinth
Eichhornia crassipes
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