The Leeward Antilles of the Dutch Caribbean are home to a tremendous number of marine fish species, because of the thriving coral reef ecosystems along their coastlines. What fewer people know is that Aruba, Bonaire and Curaçao are also home to a very common and abundant, endemic freshwater fish species; Poecilia vandepolli, locally known as ‘molly’ or ‘machuri’. All the more reason to put this species ‘in the spotlight‘ this month!
Poecilia vandepolli does not have an official common name, but is referred to as Van de Poll’s Molly. Other names are Yellowtail Molly or Dutch Antillean Molly. It’s a close relative of the famous Guppy (P. reticulata) which has been bred in all possible colour combinations imaginable and appears in many freshwater aquariums.
The name Poecilia comes from the Greek word ‘poikilos‘ which means ‘with a lot of colours’.
The multi-coloured appearance also occurs in P. vandepolli: grayish-brown as well as orange-bellied specimens are abound. Even yellowish fish with blue iridescent sides have all been described within the same population. Speckled individuals of this species have been found on Aruba and Curaçao. In some colour-types the pigmentation at the base of the dorsal fin forms a so-called ‘humeral blotch’, an enlarged dark spot often located behind the gill cover.
There are 40 known species in the genus Poecilia and they are collectively known as ‘Mollies’. All species in the Poecilia genus are live-bearing, which means that the females don’t lay eggs, but fertilisation and development of the eggs takes place inside the body. After a period of a few weeks, the offspring ‘hatch’ and are released fully developed into the water.
Poecilia vandepolli is a euryhaline fish, meaning it can not only live in freshwater habitats (see picture below), but can also survive in brackish, and saltwater. They have even been found to tolerate the hypersaline conditions of the water that occurs in saliñas. This trait has evolved due to the climatic cycle on the Leeward Antillean islands. During the dry season, the fish migrate towards the ocean when their freshwater habitat (often) dries up completely, only to swim up the re-emerging freshwater streams in the beginning of the next wet season and repopulate the newly formed freshwater basins.
Just like its relative the Guppy is used in other parts of the world, P. vandepolli makes a welcome contribution to mosquito control on the Leeward islands of the Dutch Caribbean. Adding just a few P. vandepolli to the stagnant waterbodies that mosquitos require for their larval stage, can help contain the mosquito problem. The fish reproduce and feed off mosquito larvae and algae and so the population maintains itself. Many people on the islands have large, often underground cisterns in their backyards to contain rainwater for the garden in times of drought. These cisterns prove to be the perfect habitat for mosquitos… and the fish! There are all kinds of environmentally unfriendly chemical agents for mosquito control on the market, but why do that when a couple of tiny fish will solve the problem too?
On St. Maarten, P. vandepolli has been introduced many years ago for this very reason. These days, the introduction of exotic species for pest control or for any other reason is no longer accepted practice. Throughout history, there have been plenty of examples of exotic species, originally introduced to deal with a pest species, that eventually have had a devastating effect on the entire native ecosystem. With P. vandepolli, this problem can be sidestepped, since this species is native to the Leeward islands. Therefore, to further curb the problem of invasive species, whenever possible, always use the endemic P. vandepolli on Aruba, Bonaire and Curaçao to control mosquitoes, and not the exotic Guppy.
- Fishes running out of water: Identifying traits for adapting to climate change.
- Ho, A.L.F.C. (2013) The endemic molly of the ABC islands: van de Poll’s molly (Poecilia vandepolli). Amazonas 2(5):44-51
- Debrot, A.O. (2003). A review of the freshwater fishes of Curaçao, with comments on those of Aruba and Bonaire. Carib. J. Sci. 39(1): 100-108