crustacean prey over mosquitos, highlighting their potential for impact on a broad
range of invertebrate taxa.
Poecilia reticulata and X. helleri are popular aquarium fishes native to freshwater
and brackish water habitats in Central America. Poecilia reticulata was first introduced to the Western Cape from Barbados in 1912 for mosquito control but failed to
establish as it is intolerant of temperatures below 15
C (de Moor and Bruton 1988).
Subsequent imports by the pet trade of P. reticulata continue because they are
popular aquarium fishes. All naturalised populations in the wild occur warmer
coastal regions of the country and are likely to be a result of direct releases by
aquarists (Ellender and Weyl 2014). Impacts of established populations have not
been studied in South Africa, but evidence from around the globe has shown that
P. reticulata invasions deplete native fauna and alter ecosystems (El-Sabaawi et al.
2016).
Xiphophorus helleri and X. maculatus were likely introduced into the wild by
aquarists releasing unwanted fish, and naturalised populations are restricted to urban
environments in sub-tropical parts of KwaZulu-Natal (Ellender and Weyl 2014).
Impacts, although poorly explored, are likely to be similar to those observed for
G. affinis and P. reticulata.
Salmonidae
The family Salmonidae includes trouts and salmons, which are popular table and
sport fishes. As popular angling species, they are among the earliest intentionally
introduced fishes in the country. Atlantic Salmon Salmo salar, Brown Trout Salmo
trutta, Brook Trout Salvelinus fontinalis and Rainbow Trout Oncorhynchus mykiss
were introduced into the country in the late 1800s, and were released into the wild to
develop angling opportunities for species familiar to European settlers (Ellender and
Weyl 2014). Salmo salar and S. fontinalis failed to establish in the wild, but S. trutta
and O. mykiss naturalised and are popular with recreational anglers (Weyl et al.
2017a, b).
Onchorhynchus mykiss, characterised by an iridescent pinkish lateral band, is
native to North America but was introduced to South Africa for sport fishing in 1897.
This species was subsequently released in many localities to sustain recreational
angling (Ellender et al. 2014). In impoundments these fish can attain weights of 6 kg
but fishes from naturalised populations in rivers seldom attain weights greater than
1 kg (Skelton and Weyl 2011). Naturalised populations are limited to cool, clear
mountain streams, where their downstream spread is mediated by temperature
(Shelton et al. 2018).
Salmo trutta is distinguished from O. mykiss by its brown colour and the presence
of large reddish brown spots on its flanks. Salmo trutta were imported into
South Africa from their native range in Europe in 1890. As is the case with
O. mykiss, S. trutta were released into streams in mountainous regions. Salmo trutta
has established in some mountain streams where maximum temperatures seldom
exceed 17
C and, because of their lower tolerance to high temperature, they are not
as widespread as O. mykiss (Weyl et al. 2017a, b).
Oncorhynchus mykiss and S. trutta are generalist predators that through dietary
interactions can impact on recipient ecosystems at numerous trophic levels (Weyl
174
O. L. F. Weyl et al.
range of invertebrate taxa.
Poecilia reticulata and X. helleri are popular aquarium fishes native to freshwater
and brackish water habitats in Central America. Poecilia reticulata was first introduced to the Western Cape from Barbados in 1912 for mosquito control but failed to
establish as it is intolerant of temperatures below 15
C (de Moor and Bruton 1988).
Subsequent imports by the pet trade of P. reticulata continue because they are
popular aquarium fishes. All naturalised populations in the wild occur warmer
coastal regions of the country and are likely to be a result of direct releases by
aquarists (Ellender and Weyl 2014). Impacts of established populations have not
been studied in South Africa, but evidence from around the globe has shown that
P. reticulata invasions deplete native fauna and alter ecosystems (El-Sabaawi et al.
2016).
Xiphophorus helleri and X. maculatus were likely introduced into the wild by
aquarists releasing unwanted fish, and naturalised populations are restricted to urban
environments in sub-tropical parts of KwaZulu-Natal (Ellender and Weyl 2014).
Impacts, although poorly explored, are likely to be similar to those observed for
G. affinis and P. reticulata.
Salmonidae
The family Salmonidae includes trouts and salmons, which are popular table and
sport fishes. As popular angling species, they are among the earliest intentionally
introduced fishes in the country. Atlantic Salmon Salmo salar, Brown Trout Salmo
trutta, Brook Trout Salvelinus fontinalis and Rainbow Trout Oncorhynchus mykiss
were introduced into the country in the late 1800s, and were released into the wild to
develop angling opportunities for species familiar to European settlers (Ellender and
Weyl 2014). Salmo salar and S. fontinalis failed to establish in the wild, but S. trutta
and O. mykiss naturalised and are popular with recreational anglers (Weyl et al.
2017a, b).
Onchorhynchus mykiss, characterised by an iridescent pinkish lateral band, is
native to North America but was introduced to South Africa for sport fishing in 1897.
This species was subsequently released in many localities to sustain recreational
angling (Ellender et al. 2014). In impoundments these fish can attain weights of 6 kg
but fishes from naturalised populations in rivers seldom attain weights greater than
1 kg (Skelton and Weyl 2011). Naturalised populations are limited to cool, clear
mountain streams, where their downstream spread is mediated by temperature
(Shelton et al. 2018).
Salmo trutta is distinguished from O. mykiss by its brown colour and the presence
of large reddish brown spots on its flanks. Salmo trutta were imported into
South Africa from their native range in Europe in 1890. As is the case with
O. mykiss, S. trutta were released into streams in mountainous regions. Salmo trutta
has established in some mountain streams where maximum temperatures seldom
exceed 17
C and, because of their lower tolerance to high temperature, they are not
as widespread as O. mykiss (Weyl et al. 2017a, b).
Oncorhynchus mykiss and S. trutta are generalist predators that through dietary
interactions can impact on recipient ecosystems at numerous trophic levels (Weyl
174
O. L. F. Weyl et al.