WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2018 59 native fishes, occupying open niches vulnerable ecosystems, causing competitive exclusion, and eventually leading to up to 48 percent of fish extinctions (Harrison and Stiassny 1999, MacKinnon 2002, Ricciardi 2004, Clavero and Garcia-Berthou 2006). • IAFS may cause biotic homogenization – the interbreeding or hybridization with locally compatible fish species that leads to a loss of their biological distinctiveness or identity at functional, genetic and taxonomic levels. This leads to the loss of “pure” native species that often lose to more aggressive hybrids that may have increased bio-invasive potential (Huxel 1999, Mooney and Cleland 2001, Oldgen and Rooney 2006). Biodiversity losses are greater in freshwater ecosystems than in terrestrial environments (Jenkins 2003). • IAFS may carry new and exotic diseases (Pickrell 2004). Some diseases such as viral hemorrhagic septicemia that causes bleeding and damage to vital organs of fish has been documented to be transmitted through IAFS and affect fish populations (Browser 2017). Certain species such as the freshwater snail Biomphalaria straminea can be vectors of disease such as schistosomiasis (Ferrari and Hoffman 1992). • IAFS may cause habitat degradation and skew food production that are necessary for economically important fishes in aquatic habitats by changing nutrient dynamics (Hermoso et al. 2011, Capps and Flecker 2013). This leads to less food and nutrients available for fish and other species in the environment. • Some species such as from the genus Pterygoplichthys, more commonly known as janitor fish, cause damage to riverbanks and fishing implements of commercial fishermen, affecting their livelihoods (Huballa et al. 2008, Guerrero 2014). • Invasive species may influence and shape evolution; it has been previously believed that evolution takes a long time (Hulme and Roux 2016) but studying IAFS shows that they can alter evolutionary pathways of native fish due to various ecological selection pressures The Philippines is one of the centers of global fish diversity due to its archipelagic shape and tropical position, providing a wide array of ecosystems to sustain a massive assortment of fish species. This diversity is a vital resource for the country because fish provide income, nutrition and international export from the fishing nation (Alima and Patricio 2010). Although rapid population increase leading to pollution, combined with global climate change, have caused extensive damage to inland and coastal aquatic habitats, the alarming increase in proliferation of invasive alien fish species (IAFS) is fast becoming a threat to endemic and indigenous wildlife in national waters (Joshi 2006). There are many pathways for the spread of IAFS and an understudied branch of their proliferation is the escape of ornamental fish into native waters. What are Alien Fish and What is Their Impact? “Alien” fish are non-native species that are introduced into marine or freshwater systems deliberately or accidentally for biological control, commerce, food production, sport or ornamentation (Guerrero 2014). In over a century, more than 60 species have been introduced into Philippine waters and have become a mainstay in the majority of the major streams and rivers of the country, thriving with their own wild populations (Joshi 2006, Guerrero 2014). Most of these species are hardy and quick to adapt, having the ability to thrive in local areas that are not part of their natural distribution range. The magnitude of damage from these species is difficult to quantify, owing to multifactorial impacts on an array of colonized habitats (Nghiem et al. 2013). Exotic species reproduce and establish themselves quickly in new habitats, altering the natural animal and plant composition of these ecosystems. These alterations raise ecological, economic, evolutionary and health concerns: • IAFS can cause alterations in native fish populations, contributing to the production loss of commercial fish species through predation. IAFS are also implicated as a leading cause of displacement of Aliens from Aquariums Zomesh A. Maini, Vikas Kumar and Janice A. Ragaza (CONTINUED ON PAGE 60) The spotted knifefish Chitala ornata can consume 7 kg of fish and shellfish per day, wrecking aquafarms and nurseries in Laguna de Bay, Philippines. Photo: J.A. Ragaza. Arapaima (Arapaima gigas), native to South America, is one of the largest freshwater fishes in the world. Photo: J.A. Ragaza.
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