Poecillids are highly specialised and well adapted to surviving in highly undesirable conditions. Because of this they have been able to establish populations in many areas where have been released. There are two species of poecillids in New Zealand that have established populations in thermal waters. Sailfin mollies (Poecilia latapinna) are found the South Taupo wetlands near Tokaanu, and the Guppies (Poecilia reticulata) are found at multiple sites in and near Reporoa. These fish were known to have been present in New Zealand since at least the 1930s. However, there has been very little study carried out on their ecology in New Zealand. In order to fill this knowledge gap, a study was carried out to assess the approximate population numbers and the health of each of these species. As well as this it was unknown what exactly these species were feeding on in the thermal waters; therefore a gut analysis was carried out to find out which species of invertebrates if any are part of the diets. It was found that both species have very healthy populations in New Zealand thermal waters; as well as this their diets vary considerably between both species. The sex ratios for both species in New Zealand are quite different from those found in other feral populations. The current populations are found to be of reasonable size especially the Sailfin Mollies; which shows just how well adapted these species have become to the New Zealand conditions. Because of the apparent lack of knowledge of these species numbers and feeding habits in New Zealand and the well-known ability of these species to colonise new habitats; it is important to understand the current population health to allow for any potential management programs in the future.