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Maximum size : 6 cm

Dusky Millions Fish - Phalloceros caudimaculatus : Complete Fish Profile & Care Guide

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The Dusky Millions Fish is attractive, hardy and relatively easy to breed. As a result, they are reasonably popular in the aquarium hobby. The Dusky Millions Fish is best kept in a species-only aquarium in a group of 6 to 8 individuals, ensuring you have two to three females to every male, as this will stop any single female from taking the full extent of the male's continual harassment. These fish are peaceful, so you could keep them in a community aquarium alongside other peaceful species that also appreciate cooler water conditions, such as Danios, White Cloud Mountain Minnows and Ricefish. However, you should avoid housing them with species with intricate finnage or much larger aggressive fish that may intimidate or out-compete them for food. These fish prefer a heavily planted aquarium with gentle filtration and water movement to mimic their natural environment. It would be best to choose robust or fast-growing plants, as many soft-leaved plants will be grazed upon; however, this may not necessarily be a problem if they are well fed. Floating plant species such as duckweed or water lettuce may be used to help dim the lighting in the aquarium. The Dusky Millions fish is very sensitive to changes in water chemistry; therefore, any adjustments in parameters must be carried out slowly. It would be best if you also took care when performing water changes, frequently perform minimal amounts, but gradually add the new water. For this reason, this species is only recommended for advanced aquarists. The Dusky Millions Fish has a silvery body with a small, dark, vertical elongated mark under the dorsal fin and black patches on the fins. The male bodies are distinctively speckled with many irregular black blotches and spots, whereas the females only display a few. In addition, you may find some individuals with a yellowish hint in their bodies.

Dusky Millions Fish Photos

Sexual Dimorphism

It is very simple to differentiate between the male and female Dusky Millions Fish. The females are much bigger than the males and have fewer blotches. In contrast, the males are smaller, have more speckling than the females and possess an evident gonopodium.
Featured Male
Featured Female
Male Female

Quick Facts

Scientific NamePhalloceros caudimaculatus
Year Described1868
Other NamesSpeckled mosquitofish, one-spot livebearer, Speckled Livebearer, Leopardfish
OriginsBrazil Argentina Uruguay Paraguay
Max Size6 cm
Aquarium LevelAll Levels
DifficultyIntermediate - Advanced
Best kept asGroups 6+
Lifespan1 - 2 years

Water Parameters

Water TypeFreshwater/Brackish
PH6.0 - 8.0
GH5 - 20
TDS90 – 447
64 - 72
17.8 - 22.2

Natural habitat

The Dusky Millions Fish is endemic to northern Argentina, Rio de Janeiro, Uruguay and Paraguay in eastern and southern Brazil in South America. However, these fish have been introduced to many other countries primarily for Mosquito Larvae control, leading to them becoming an invasive species. These fish inhabit slow-flowing streams, rivers, and ponds, usually with dense vegetation. Nevertheless, it is incredibly adaptable and can thrive in numerous environments. You may also find some populations in slightly brackish water.

How to breed the Dusky Millions Fish

The Dusky Millions Fish are straightforward to breed. Once fertilisation has occurred, the female gestates for around four weeks, depending on the temperature. After this time, she will give birth to up to 50 free-swimming fry, although younger females will give birth to fewer numbers. The adults will not usually prey on the young; however, other fish species in the same aquarium will more than likely predate on the fry if you do not separate them. A few fry will typically survive into adulthood when kept in a well-planted aquarium with lots of hiding places. You can feed the fry on finely crushed dried food, baby brine shrimp and microworms as soon as they are born.

Diet & feeding

The Dusky Million Fish is unfussy and will accept most foods you offer. These fish consume algae, small insects, insect larvae, and crustaceans in the wild. In the aquarium, you should provide your fish with frozen, live and freeze-dried foods such as baby brine shrimp, vitamin-enriched brine shrimp, mini-bloodworm, and white mosquito larvae alongside dried food such as flakes, micropellets and granules. These fish will also nibble on algae and soft-leaved plants. The occasional vegetable treat is also appreciated and very beneficial.

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