Featured Article Summary #278

Poecilia vandepolli, also called Van de Poll’s molly, is a fish native to the Caribbean islands of Aruba, Bonaire, and Curaçao. It is very common in many types of water, including fresh, brackish, salt, and very salty (hypersaline) habitats such as streams, ponds, bays, and lagoons. The fish was once considered a subspecies of P. sphenops, but later studies showed it is a separate, distinct species. It varies widely in size and color, and male fish can develop strong orange coloring, which may make them popular with aquarium keepers. They live in groups near the water’s surface, feed mainly on algae and small aquatic life, and are eaten by other fish and birds. Females give birth to live young, but survival depends on having hiding places because many fry are eaten by adults, and seasonal dry periods can wipe out freshwater populations until rains bring them back. Van Lidth de Jeude first described Poecilia vandepolli in 1887 from Curaçao and suggested an Aruba subspecies, but later researchers argued these differences were just normal variation. Over time, P. vandepolli was repeatedly treated as a subspecies (especially of P. sphenops) or questioned, until Poeser reinstated it as a full species in 1992 based on distinct traits, including the shape of male reproductive structures, coloration, body measurements, and single-pointed inner-jaw teeth. Later studies—including genetic analysis in 2016—confirmed P. vandepolli is a distinct species within the mollies and identified P. wandae as its sister species, with diversification linked to changes in sea levels and island connections. Its name honors Jacob R. H. Neervoort van de Poll, and it has no official common name, though several names are used regionally. Poecilia vandepolli can be identified by its smooth gonopodium (with fine serrations on the fourth ray) and by typical fin and scale counts. It differs from similar species (like P. sphenops and P. mexicana) by having fewer rays in the rear of the dorsal and anal fins and by sometimes showing a humeral spot behind the head, especially in freshwater fish. The species is highly variable: populations differ greatly in size, color, and markings. Differences are strongly linked to salinity—freshwater and hypersaline fish are smaller with weaker color and shorter dorsal fins, while marine fish are generally larger, more strongly colored (especially orange), and often have more and darker spots. Brackish-water fish look like freshwater ones but lack the humeral spot in males, and some Aruban males can show a small late-maturation hook on a gonopodial ray. Poecilia vandepolli is native to Aruba, Bonaire, and Curaçao in the Leeward Antilles. It has also been found in the freshwater of Saint Martin in the Windward Islands, likely introduced by Dutch settlers, but the impact there is not known. Fish populations from mainland Venezuela that were once thought to be P. vandepolli are now classified as P. koperi. Poecilia vandepolli lives in a wide range of salt conditions, from freshwater to brackish, salty, and hypersaline coastal habitats, and is especially common in the Lesser Antilles, including many ponds, rivulets, lagoons, and evaporation ponds. It prefers calm, shallow, sheltered waters (often near mangroves) with access to water, green algae, and enough low-salinity areas to escape extreme conditions. Although the fish can handle a broad temperature range, hypersaline spots can become dangerous when heat builds up or salinity spikes, so it relies on seasonal and local changes in water salinity and access to refuge.