14.2.3 Freshwater Fish
Because of their importance in aquaculture, fisheries and the global pet trade,
freshwater fishes are frequently introduced outside their native ranges as live adults
or young. Therefore, at least historically, co-introductions of novel parasites and
diseases into environments where they have not previously occurred were common.
Some of the parasites are so specialised that they are unable to infect native fishes
and their presence in the recipient environment is dependent on the presence of their
co-introduced host. Those that are able to infect native hosts can have severe
consequences, as native fish, lacking evolutionary history with alien parasites, do
not possess immune responses to infection (Taraschewski 2006).
The introduction of 27 alien fishes to South Africa has provided opportunities for
at least 23 parasitic co-introductions of ten monogeneans, eight ciliates, two cestodes, a copepod, a flagellate, and a branchiuran (Smit et al. 2017). Most (16) of
these parasites are not known to have infected native fishes (Smit et al. 2017). For
example, five ancyrocephalid monogeneans are found only on the alien Largemouth
Bass, Micropterus salmoides. Despite the almost ubiquitous presence of bass in
South African rivers (Ellender et al. 2014), these parasites have not been observed to
infect native fishes to date (Truter et al. 2017). The other seven co-introduced
parasites, however, have formed new associations with native hosts, probably
because of broader levels of generalism in their symbiotic requirements (Smit
et al. 2017). While significant impacts on the health status of novel hosts have
been documented (see Weyl et al. 2020, Sect. 6.2, on freshwater biota and impacts),
the influence of parasites on the invasion process has not been investigated in any
detail in South Africa.
Some alien fishes in South Africa have considerably lower parasite loads than in
their native ranges. In an assessment of the parasitism of largemouth bass for
example, Truter et al. (2017) documented lower parasite abundance and richness
in South Africa in comparison with native range populations. This may explain why
this species managed to invade a wide range of habitats throughout southern Africa
despite extremely low genetic diversity, resulting from a very limited number of
propagules introduced into South Africa in the late 1920s (Hargrove et al. 2017).
Similar mechanisms might be responsible for the success of rainbow trout,
Onchorhynchus mykiss, and brown trout, Salmo trutta, for which there are no
records of co-introduced parasites (see Weyl et al. 2020, Sect. 6.2).
14.2.4 Insects
South Africa’s alien entomofauna has assembled as a result of complex introduction
pathways (Giliomee 2010; Garnas et al. 2016; Janion-Scheepers and Griffiths 2020,
Chap. 7; Faulkner et al. 2020, Chap. 12). Most species were accidentally introduced,
but a small proportion were intentionally introduced, mainly as biological control
14 Biotic Interactions as Mediators of Biological Invasions
401
Because of their importance in aquaculture, fisheries and the global pet trade,
freshwater fishes are frequently introduced outside their native ranges as live adults
or young. Therefore, at least historically, co-introductions of novel parasites and
diseases into environments where they have not previously occurred were common.
Some of the parasites are so specialised that they are unable to infect native fishes
and their presence in the recipient environment is dependent on the presence of their
co-introduced host. Those that are able to infect native hosts can have severe
consequences, as native fish, lacking evolutionary history with alien parasites, do
not possess immune responses to infection (Taraschewski 2006).
The introduction of 27 alien fishes to South Africa has provided opportunities for
at least 23 parasitic co-introductions of ten monogeneans, eight ciliates, two cestodes, a copepod, a flagellate, and a branchiuran (Smit et al. 2017). Most (16) of
these parasites are not known to have infected native fishes (Smit et al. 2017). For
example, five ancyrocephalid monogeneans are found only on the alien Largemouth
Bass, Micropterus salmoides. Despite the almost ubiquitous presence of bass in
South African rivers (Ellender et al. 2014), these parasites have not been observed to
infect native fishes to date (Truter et al. 2017). The other seven co-introduced
parasites, however, have formed new associations with native hosts, probably
because of broader levels of generalism in their symbiotic requirements (Smit
et al. 2017). While significant impacts on the health status of novel hosts have
been documented (see Weyl et al. 2020, Sect. 6.2, on freshwater biota and impacts),
the influence of parasites on the invasion process has not been investigated in any
detail in South Africa.
Some alien fishes in South Africa have considerably lower parasite loads than in
their native ranges. In an assessment of the parasitism of largemouth bass for
example, Truter et al. (2017) documented lower parasite abundance and richness
in South Africa in comparison with native range populations. This may explain why
this species managed to invade a wide range of habitats throughout southern Africa
despite extremely low genetic diversity, resulting from a very limited number of
propagules introduced into South Africa in the late 1920s (Hargrove et al. 2017).
Similar mechanisms might be responsible for the success of rainbow trout,
Onchorhynchus mykiss, and brown trout, Salmo trutta, for which there are no
records of co-introduced parasites (see Weyl et al. 2020, Sect. 6.2).
14.2.4 Insects
South Africa’s alien entomofauna has assembled as a result of complex introduction
pathways (Giliomee 2010; Garnas et al. 2016; Janion-Scheepers and Griffiths 2020,
Chap. 7; Faulkner et al. 2020, Chap. 12). Most species were accidentally introduced,
but a small proportion were intentionally introduced, mainly as biological control
14 Biotic Interactions as Mediators of Biological Invasions
401