Black Molly

Adults reach 8–10 cm, with females typically larger than males. Compared with related species, this variety has more modest fins and tail. The most striking feature is a deep, coal-black body colour. Fry may be black or grey with dark spots at birth. By five months the spots usually spread to cover the whole body, though some individuals retain patches of grey-brown. Unevenly coloured fish are considered inferior by breeders and are not sold.

The wild species Poecilia sphenops lives in freshwater and brackish waters of Central and South America, from Mexico to Colombia and Venezuela. It inhabits river mouths, coastal lagoons and flowing waters where salinity often fluctuates. In nature it prefers areas with dense aquatic vegetation, which provides shelter and food.

These fish are typically peaceful and friendly. Males sometimes show increased activity, particularly during breeding, but enough shelter keeps females calm. They mix well with most warmwater species that prefer weakly alkaline water and high hardness. Good tank mates include many livebearers, rainbowfish, Corydoras catfish, some tetras and others.

For 3–4 fish, an aquarium of 80–100 litres is a good starting point. Plant the tank densely with aquatic vegetation. This selectively bred form is quite sensitive to water conditions. Keep temperature between 24–27°C, aim for neutral pH or slightly higher, and maintain hardness above 15 dGH. Deviations from these parameters can make the fish prone to disease. Sufficient oxygen in the water is critical. In heavily planted tanks, oxygen levels drop at night; boost aeration then to prevent hypoxia. Tank maintenance depends on stocking, feeding frequency and equipment, but always include a partial water change each week and removal of uneaten food and waste. Although many sources describe the black molly as easy and hardy, this view usually comes from experienced aquarists. Beginners should avoid this fish; guppies, swordtails or platies are better choices.

They readily eat most common foods: dry, frozen or live. Specialist molly pellets from major manufacturers are a good choice, as they contain all necessary nutrients including plant matter, which the fish need daily.

Although keeping this fish presents some challenges, spawning usually proceeds without delay once conditions are right. Females reach maturity at 5–7 months and males at 3–4 months, though development can take up to 6–7 months in some cases. Eggs incubate for about 30 days. Fry are born fully formed and ready to feed immediately. Raise them on specialist fry powders or suspensions, or brine shrimp nauplii. Finely crushed standard flake food also works. Adult mollies sometimes eat their own young, so move the entire brood to a separate tank at once to save them.

Poor water conditions are the root cause of most fish disease. With suitable conditions, health problems rarely arise. Deteriorating water parameters weaken the immune system and open the door to fungal, bacterial and other infections.

When buying, check for activity and clean skin: no white spots, cloudy patches or torn fins. Healthy fish school together, show curiosity and respond eagerly to food. Avoid fish with sunken bellies, signs of lethargy, or those hiding away from others, as this suggests hidden disease or stress from poor shop conditions.