World Aquaculture - September 2023

WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2023 63 Ornamental Fish Trade and Introductions The global aquatic pet trade encompasses a wide diversity of freshwater and marine organisms (Tlusty et al. 2012). Trade in ornamental fish is a multi-million dollar business with more than one hundred countries involved (Rodriguez 2000) and tropical countries face higher risk of contamination since most ornamental fish hobbyists keep tropical fish species but the risks are widespread and include all geographic regions. Global Marine Aquarium Database (GMAD) suggested that some 3.5-4.3 million fish a year, from nearly 1,500 different species, were being traded worldwide (Simcock 2016). In the USA, the majority of fish escapes have been fishes cultured for the tropical ornamental fish trade (Myrick 2002) with close to 300 species now found outside their original habitats. Established populations of some ornamental species such as Hypostomus plecostomus, mollies, guppies, platys and swordtails are well-known around tropical or subtropical ornamental fish production areas, as in Florida, Thailand, Singapore and the Philippines (Ploeg 2008). Gertzen et al. (2008) suggest the potential impact of internetbased trade in imported species may be substantial and should be investigated along with more traditional avenues of trade in aquarium fishes, as fish are being increasingly sold online. Marson et al. (2009) in a survey of aquarium owners in Canada concluded that the aquarium trade should not be overlooked as a vector for aquatic invasive species into Canadian freshwaters. A few common aquarium fish species including goldfish, common carp, Northern snakehead and rainbow snakehead have been considered to be significant threats to Canadian waters, primarily because of their demonstrated ability to survive cold water temperatures (Herborg et al. 2007, Marson et al. 2009). Alum-Udensi and Nlewadim (2019) identified a total of 45 exotic fish species within the aquarium hobby in Nigeria with varieties of Goldfish (Carassius auratus); Angelfish (Pterophyllum Scalare) and Gourami (Tricogaster leeri) being the most popular. Exotic or nonindigenous fish are those that are not naturally occurring in an environment, outside of their home range and often introduced for aquaculture, recreation, research or ornamental use. An exotic or alien species is only so outside its natural range, and may be invasive or non-invasive (Dawes 2005). Most fish introductions are intentional to broaden species diversity in aquaculture, improve local fishery potential or control unwanted pest organisms such as mosquitoes. Unintentional, accidental and/or unauthorized introductions can occur through the aquarium hobby (Kumar 2000, Alum-Udensi and Nlewadim 2017) or natural disasters such as flooding. Intentional introductions are usually done with an economic interest. The aquaculture industry in many countries is based on introduced exotic species such as clarias, trout, tilapia, Nile perch and carp. Exotic species, despite possessing some attractive characteristics both for aquaculture and ornamental fish use, may reduce the value of local species and if established in natural water bodies may become invasive, adversely affecting fish biodiversity and aquatic ecosystems (Singh and Lakra 2011). Human activity has facilitated the spread and accelerated the rate of introduction of non-indigenous species (NIS) into new environments (Hochberg and Gotelli 2005) with impacts on biodiversity of aquatic flora and fauna. Indiscriminate transfer of aquatic organisms, particularly fishes, has generated worldwide concern (Myrick 2002, Cambray 2005, Gophen 2015). They may compete with indigenous fishes for food and habitat, prey directly on fish, introduce new diseases and parasites, result in the production of hybrids causing genetic ‘erosion’ of indigenous species, and degrade the physico-chemical nature of aquatic ecosystems (Kumar 2000). Whether introduced accidentally or deliberately into a natural environment, Invasive Aquatic Species (IAS) threaten the ecological stability of invaded habitats and native species therein, as these are highly sensitive to various interactions with these non-native organisms (FAO 2016). Exotic Fish Species Introductions and Risks to Biodiversity and Ecosystems: a Review and Nigerian Perspectives Anthony A. Nlewadim and O. Alum-Udensi (CONTINUED ON PAGE 64) The aquarium hobby is often the source of unintentional, accidental and/or unauthorized introductions of exotic fishes. Photo by C. Greg Lutz