America are mostly insects that were intentionally introduced and released for the
biological control of alien aquatic plants or molluscan stowaways on imports of
aquarium plants (Picker and Griffiths 2011). Escape from captivity has been rare
(one fish and one crayfish) and direct introductions for fisheries and aquaculture
(49% of taxa), biological control (19%), and stowaways or contaminants of international trade (22%) are the most common vectors for introduction into the wild
(Fig. 6.1c).
Although the pet trade has been a pathway for the direct introduction of hundreds
of alien freshwater fishes (Box 12.1 in Faulkner et al. 2020, Chap. 12; van der Walt
et al. 2017), only four have naturalised, mostly in close association with humans
(Ellender and Weyl 2014). Examples include populations of Guppy Poecilia
reticulata in urban streams and the occasional presence of naturalised Goldfish
Carssius auratus populations in urban ponds and impoundments (Ellender and
Weyl 2014). There are, however, exceptions. Vermiculated Sailfin Catfish
Pterygoplichthys disjunctivus escaped from captivity in the upper Mthlatuze catchment and then invaded the Nseleni River via an artificial connection between the two
rivers (Jones et al. 2013). Even more widespread is the Quilted Melania Terebia
granifera, a snail that was most likely introduced into the country as a stowaway
with aquatic aquarium plants and now occurs widely in subtropical rivers and
estuaries (Picker and Griffiths 2011).
Fisheries and aquaculture were the motivation for the importation of at least 12 of
the naturalised alien fishes (Ellender and Weyl 2014) and 1 crayfish (Nunes et al.
2017). Most naturalised populations of alien fishes in South Africa are the result of
direct introductions into the wild (Ellender and Weyl 2014). The desire to develop
opportunities for recreational angling was the main driver for the construction of fish
hatcheries in the early to mid-twentieth century. Once constructed, imported fish
were bred and their offspring released directly into suitable environments by government agencies, acclimatisation societies and angling organisations (Ellender et al.
2014). Fishes introduced for this purpose include Common Carp Cyprinus carpio
(in 1859), Brown Trout Salmo trutta (in 1892), Rainbow Trout Oncorhynchus
mykiss (in 1897) and Largemouth Bass Micropterus salmoides (in 1928) (Ellender
and Weyl 2014). Direct escape from fish farms is also an important invasion
pathway. For example, the invasion of the Olifants and Limpopo rivers by Silver
Carp Hypophthalmichthys molitrix originated from a government fish farm at Marble
Hall (Ellender and Weyl 2014) and the escape of Redclaw Crayfish Cherax
quadricarinatus from an aquaculture facility in Swaziland was responsible for its
naturalisation and subsequent spread into South Africa (Nunes et al. 2017). As was
the case with the pet trade, contamination of introduced fishes and subsequent
infection of other species on fish farms resulted in the spread of many parasitic
organisms together with their fish and crayfish hosts (Smit et al. 2017).
Several releases of biological control agents also resulted in the naturalisation of
several alien taxa. The direct release of aquatic insects as biological control agents is
associated with stringent testing of host specificity (Hill and Coetzee 2017). In
contrast to the careful screening, and consequent impressive safety record of alien
plant biological control (van Wilgen et al. 2013), the misguided release of Grass
6 Alien Freshwater Fauna in South Africa
161
biological control of alien aquatic plants or molluscan stowaways on imports of
aquarium plants (Picker and Griffiths 2011). Escape from captivity has been rare
(one fish and one crayfish) and direct introductions for fisheries and aquaculture
(49% of taxa), biological control (19%), and stowaways or contaminants of international trade (22%) are the most common vectors for introduction into the wild
(Fig. 6.1c).
Although the pet trade has been a pathway for the direct introduction of hundreds
of alien freshwater fishes (Box 12.1 in Faulkner et al. 2020, Chap. 12; van der Walt
et al. 2017), only four have naturalised, mostly in close association with humans
(Ellender and Weyl 2014). Examples include populations of Guppy Poecilia
reticulata in urban streams and the occasional presence of naturalised Goldfish
Carssius auratus populations in urban ponds and impoundments (Ellender and
Weyl 2014). There are, however, exceptions. Vermiculated Sailfin Catfish
Pterygoplichthys disjunctivus escaped from captivity in the upper Mthlatuze catchment and then invaded the Nseleni River via an artificial connection between the two
rivers (Jones et al. 2013). Even more widespread is the Quilted Melania Terebia
granifera, a snail that was most likely introduced into the country as a stowaway
with aquatic aquarium plants and now occurs widely in subtropical rivers and
estuaries (Picker and Griffiths 2011).
Fisheries and aquaculture were the motivation for the importation of at least 12 of
the naturalised alien fishes (Ellender and Weyl 2014) and 1 crayfish (Nunes et al.
2017). Most naturalised populations of alien fishes in South Africa are the result of
direct introductions into the wild (Ellender and Weyl 2014). The desire to develop
opportunities for recreational angling was the main driver for the construction of fish
hatcheries in the early to mid-twentieth century. Once constructed, imported fish
were bred and their offspring released directly into suitable environments by government agencies, acclimatisation societies and angling organisations (Ellender et al.
2014). Fishes introduced for this purpose include Common Carp Cyprinus carpio
(in 1859), Brown Trout Salmo trutta (in 1892), Rainbow Trout Oncorhynchus
mykiss (in 1897) and Largemouth Bass Micropterus salmoides (in 1928) (Ellender
and Weyl 2014). Direct escape from fish farms is also an important invasion
pathway. For example, the invasion of the Olifants and Limpopo rivers by Silver
Carp Hypophthalmichthys molitrix originated from a government fish farm at Marble
Hall (Ellender and Weyl 2014) and the escape of Redclaw Crayfish Cherax
quadricarinatus from an aquaculture facility in Swaziland was responsible for its
naturalisation and subsequent spread into South Africa (Nunes et al. 2017). As was
the case with the pet trade, contamination of introduced fishes and subsequent
infection of other species on fish farms resulted in the spread of many parasitic
organisms together with their fish and crayfish hosts (Smit et al. 2017).
Several releases of biological control agents also resulted in the naturalisation of
several alien taxa. The direct release of aquatic insects as biological control agents is
associated with stringent testing of host specificity (Hill and Coetzee 2017). In
contrast to the careful screening, and consequent impressive safety record of alien
plant biological control (van Wilgen et al. 2013), the misguided release of Grass
6 Alien Freshwater Fauna in South Africa
161