Are fancy guppies ( Poeciliareticulata Peters, 1859) invasive?

Guppies ( Poecilia reticulata Peters 1859) have been introduced to Sri Lanka in the early 1970s to combat the menace of Malaria. Due to their rapid range expansion in natural waterways, guppies are labeled as an ‘invasive species.’ Guppies are also popular in the ornamental fish trade where a wide variety of ornamental guppy varieties with attractive colour and fin patterns have been produced through selective breeding; they are commonly known as ‘fancy guppies’ or ‘saree guppies’. Since there are some concerns over the invasiveness of these fancy guppies into natural water bodies in Sri Lanka, the potential invasiveness of two common fancy guppy varieties with long caudal fins viz. black guppies and yellow guppies, was assessed under laboratory conditions using their specific growth rates (SGR) and critical swimming speeds (U crit ). Results in the present study showed that the SGR of black guppies (1.0 % g day -1 ), and yellow guppies (0.99 % g day -1 ) were significantly lower (p -1 ). Further, the U crit of the black guppies (23.8 cm s -1 ), and yellow guppies (26.8 cm s -1 ) were significantly lower (p -1 ). Since the long caudal fins significantly reduced  the swimming speed (p