Current and future risk of invasion by non-native freshwater fishes in a mega-biodiversity country: the Philippines

The Philippines is a mega-biodiversity country hosting a vast number of aquatic species of which most are endemic. With over 7,100 islands making up its territory, the Philippines are home to a remarkable array of fish species. These play a vital role in enriching the country's inland waters biodiversity and some of them are of high economic and commercial value. However, this extremely rich biodiversity is on the brink of collapse. Research in the Philippines has primarily focused on marine and terrestrial ecosystems, highlighting a significant gap in the study of inland waters and its freshwater fishes. In total, 374 freshwater fish species belonging to 29 orders and 78 families have been documented in the Philippines. This large number of fish species faces high extinction risks due to various human-induced impacts including habitat destruction, overfishing and the presence of introduced species. This study investigates the risk of invasiveness of all 64 introduced freshwater fish species currently present in the Philippines. Of these species, 65.6% and 70.3% were ranked as carrying a high or very high risk of invasiveness under current and future climate conditions, respectively. The highest risk species were goldfish Carassius auratus, Indonesian snakehead Channa micropeltes, largemouth black bass Micropterus salmoides, pirapitinga Piaractus brachypomus, vermiculated sailfin catfish Pterygoplichthys disjunctivus and Amazon sailfin catfish Pterygoplichthys pardalis. Given the high conservation value of Philippine freshwater ecosystems, efforts are needed from stakeholders and environmental managers in the mitigation and prevention of the detrimental impacts of the invasive fish species already present, and preventative measures are required to counteract the introduction of any additional non-native species. The results of this study, which represents the first comprehensive risk screening for a specific group of organisms in a country, will serve as a foundation for developing shared regulations to control the international trade of the non-native fish species at higher risk of invasion.