The effects of introduced tilapias on native biodiversity

Abstract

ABSTRACT1. The common name 'tilapia' refers to a group of tropical freshwater fish in the family Cichlidae (Oreochromis, Tilapia, and Sarotherodon spp.) that are indigenous to Africa and the southwestern Middle East. Since the 1930s, tilapias have been intentionally dispersed worldwide for the biological control of aquatic weeds and insects, as baitfish for certain capture fisheries, for aquaria, and as a food fish. They have most recently been promoted as an important source of protein that could provide food security for developing countries without the environmental problems associated with terrestrial agriculture. In addition, market demand for tilapia in developed countries such as the United States is growing rapidly.2. Tilapias are well-suited to aquaculture because they are highly prolific and tolerant to a range of environmental conditions. They have come to be known as the 'aquatic chicken' because of their potential as an affordable, high-yield source of protein that can be easily raised in a range of environments } from subsistence or 'backyard' units to intensive fish hatcheries. In some countries, particularly in Asia, nearly all of the introduced tilapias produced are consumed domestically; tilapias have contributed to basic food security for such societies.3. This review indicates that tilapia species are highly invasive and exist under feral conditions in every nation in which they have been cultured or introduced. Thus, the authors have concluded that, despite potential or observed benefits to human society, tilapia aquaculture and open-water introductions cannot continue unchecked without further exacerbating damage to native fish species and biodiversity. Recommendations include restricting tilapia culture to carefully managed, contained ponds, although exclusion is preferred when it is feasible. Research into culture of indigenous species is also recommended.

Tradeoffs among Ecosystem Services Associated with Global Tilapia Introductions

“…Global databases of introductions indicate relatively few negative impacts for many freshwater fish species particularly relative to the economic value of their production (Gozlan, 2008). Different authors have, however, reached different conclusions about the extent of undesirable impacts on ecosystems relative to the benefits of aquaculture and fisheries, particularly those based tilapia (Leveque, 2002;Canonico et al, 2005;Gozlan, 2008;Brummett and Ponzoni, 2009;De Silva et al, 2009;Vitule et al, 2009). Since 2002 tilapia (Cichlidae: primarily of genera Oreochromis, Tilapia, and Serranochromis.…”

“…Changes in the biotic components of an ecosystem, including changes caused by species introduction, may increase some services while simultaneously decreasing others (Hooper et al, 2005;Lodge et al, 2012). Specifically, increasing tilapia production may cause a decrease in populations of harvestable native species, a decrease in habitat, or recreational and cultural ecosystem services linked to the native species harmed by tilapia (Canonico et al, 2005). Differing opinions on the type of ecosystem services provided or affected by tilapia prevent a comprehensive policy framework for the management of this species (Redpath et al, 2013).…”

“…The ecosystem service tradeoffs potentially caused by tilapia production have been the subject of previous reviews that documented undesirable ecological effects (Pullin et al, 1997;Canonico et al, 2005). For example, tilapia are considered to be the proximate cause of declines in many native fishes: desert pupfish (Cyprinodon macularius) in the South West United States (Black, 1980;Varela-Romero et al, 2000), Sinarapan (Mistichthys luzonensis) from Lake Buhi in the Philippines (Gindelberger, 1981), and various native cichlids that once comprised important components of fisheries harvests in Lake Nicaragua (McKaye et al, 1995) and Lake Victoria (Mkumbo and Ligtvoet, 1992;Goudswaard et al, 2002).…”

“…Assessments of tilapia impacts range from no negative impacts to extremely harmful (Canonico et al, 2005;Gozlan, 2008). This range of perceptions is perpetuated because areas where tilapia have been introduced for culture and capture fisheries are concentrated where resources to support ecological research are limited (Canonico et al, 2005;UNESCO, 2007;De Silva et al, 2009;Josupeit, 2010;Skelton & Swartz, 2011;Amano and Sutherland, 2013). It is likely that the absence of evidence for ecological effects is often substituted in management and policy decisions for evidence of the absence of ecological effects, in which case the monetized value of tilapia production may drive perceptions and decisions about tilapia introduction (L€ ovei et al, 2012).…”

“…The life-history traits of tilapia that have made them an aquacultural success (e.g., rapid somatic and population growth, wide environmental tolerances) are the same traits often associated with invasive species (Bruton and van As, 1986;Lorenzen, 2000;Norrgren et al, 2000;Canonico et al, 2005). These and other traits differ between common species of tilapia, such that different species might be expected to have different ecological effects.…”