Tai provides advice on how best to build a natural aquarium for the wonderful mollies (Poecilia sphenops).
Please could you give me some advice on setting up a biotope tank for black mollies? I’ve always loved these fish, and I'd like to try keeping them in a more natural environment.
PHIL BOOTH
Tai Strietman's advice on molly biotopes
Black mollies (Poecilia sphenops), are very popular in the hobby, but they are an ornamental strain. In their natural habitats, there are no naturally occurring black examples – although black individuals are found due to deliberate introduction. Instead, wild P. sphenops have a silver-copper or metallic greenish hue to the bodies, with yellow edging on the fins.
Wild colouration of Poecilia sphenops - Photo by Shutterstock
They have a large distribution from Colombia and Venezuela to Mexico, with some isolated populations found on Caribbean islands. They live mostly in coastal creeks, in warm, shallow water which can range from fresh to brackish, although they can even be found in marine conditions near the coast.
They can be encountered in creeks, streams, ponds, pools, tidal marshes, coastal lagoons and mangrove environments, so the list of potential biotopes is considerable. It might be best to pick just one or two examples for inspiration. You could create a shallow river display, with water flowing over gravel and water-worn rocks covered in algae which the mollies will graze on. Perhaps also add some branchy wood to offer cover and break up lines of sight – mostly to give the females a chance to dodge the over-zealous male gaze for a while.
I created a miniature version of this for wild Endler’s guppies – I’ve included a photo of that set-up below – and you could easily do an expanded version for your mollies. You can use the Río Grande de Matagalpa of central Nicaragua as the inspiration for such a layout.
Photo by Tai Strietman
A wetlands pond biotope
An alternative would be to create a coastal wetlands pond design, with a thick layer of soft substrate. A pond plant soil would work well, and the mollies will love grubbing about in. Throw in plenty of leaf litter and some seed ponds, with a few twiggy bits of wood.
You could fill the display with a dwarf pond lily species such as Nymphaea pygmaea "Alba" or Nymphoides peltata, as a stand-in for Central American species. The lily stems and pads would provide cover for the fishes and algae will grow on the stems, which the mollies will appreciate. Some handfuls of hornwort (Ceratophyllum demersum), pictured below, will grow quickly and provide a refuge for any fry.
Related article: The beginners guide to growing healthy aquarium plants.
Photo by Shutterstock
Don’t worry if your mollies are black rather than the wild forms. If you like the ornamental black strain (pictured below), that’s just fine, and they will still feel at home in one of these biotopes.
Photo by Shutterstock
Common Molly Factfile
Scientific name: Poecilia sphenops, however, aquarium strains are often hybrids.
Size: Females can reach 12cm (4.7”), males smaller at 8cm (3.1”).
Origin: Central and South America, especially Mexico and Venezuela.
Habitat: Occurs in a wide range of habitats and environmental conditions. They thrive in freshwater, brackish and marine conditions. Slow-moving coastal rivers and streams, pools and flooded ditches are common places to encounter them.
Tank size: 90x30x30cm (36x12x12”)
Water requirements: A pH of 7.5-8.5 with moderate hardness (10-25°H) will work well.
Temperature: 22-28°C (72-82°F)
Temperament: Relatively peaceful, but can be a little too boisterous for the calmest species. Males often spar and display to one another.
Feeding: Omnivorous and adaptable but ensure to include plenty of plant-based foods.
Availability & cost: Common line bred strains are available routinely at around £3 each. Rarer strains can cost up to £50 a pair. For wild Poecilia sphenops livebearer auctions are probably your best bet.