Sailfin Molly

The sailfin molly takes its name from the male's spectacular dorsal fin, a genuine sail raised during courtship and in disputes between rivals. A member of the Poeciliidae, it shares livebearing reproduction with the guppy and the platy but grows far larger, reaching 15 cm. Females are bulkier, plainer in colour, and carry an ordinary dorsal. The wild coloration is grey-green, flecked with rows of dark spots and shot through with blue and orange in displaying males. The species inhabits the Atlantic and Gulf coastal plain from North Carolina down to Veracruz, favouring still, well-vegetated water: estuaries, lagoons, river deltas, ditches and mangrove swamps, where it grazes on algae and biofilm. Its salt tolerance is remarkable, reaching 87 ppt, well beyond full seawater, yet in the aquarium it is hardness and alkalinity, not salt, that govern its health. Allow 100 litres for a trio and keep one male to two or three females, since a lone female would be worn down by his constant attentions. The water must be genuinely hard and alkaline. Feed a plant-based diet of spirulina, algae wafers and blanched vegetables; too much meaty food brings digestive trouble. Breeding is spontaneous, with broods of 10 to 140 fry. Mature fish may pick at smaller tankmates.