Use of Larvivorous Fish in Biological and Environmental Control of Disease Vectors - Biological and Environmental Control of Disease Vectors - page 32

3.4 Negative Impact of the
Introduction of Larvivorous Fish in
Mosquito Control Operations

Rupp, 1996; Rehage et al ., 2005; Walton,
2007). Mosquito fi sh introduced in 1922 into
southern California have now become a threat
to native fi sh species that share similar habitats.
A particular problem are Cyprinodontidae
because of their ecological advantages, which
include fast growth, early maturity, viviparity
(Barrier and Hicks, 1994; Vargas and deSostoa,
1996) and high food consumption per day
(Wurtsbaugh and Cech, 1983). In addition to
competition for resources, species of Gambusia
are aggressive and often attack fi sh more than
twice their own size and mass (Gophen et al .,
1998; Rowe, 1998). This can result in damage
to the fi ns and scales, leaving the fi sh susceptible
to bacterial and protozoan diseases.
Considering their non-target ef ects and
ability to spread, several ecologists have
questioned the use of larvivorous fi sh as
biological control agents, especially when
introduced as exotic species (Moyle, 1976;
McKay, 1984; Simberlof and Stiling, 1996). The
introduction of Gambusia into either riverine or
large lake systems (Kolar and Lodge, 2000) or
into temporary and permanent wetlands (Leyse
et al ., 2004) can cause rapid decline in a variety
of small indigenous fi sh species (Courtenay
and Mef e, 1989; Howe et al ., 1997; Ivantsof
and Aarn, 1999), amphibians (Morgan and
Buttemer, 1996; Webb and Joss, 1997; Goodsell
and Kats, 1999; Komak and Crossland, 2000)
and invertebrates like zooplankton (Margaritora,
1992), dragonfl y nymphs (Rowe, 1987),
damselfl ies (Englund, 1999) and fairy shrimp
(Leyse et al ., 2004). The gut content analyses of
some larvivorous fi sh have shown the presence
of other dietary items than mosquito larval
remnants (Kumar, 2005). Wu et al . (1991) high-
lighted the advantages of mosquito biocontrol
by rearing edible fi sh in rice fi elds, but their
application in rice fi elds did not always yield the
positive results anticipated. Culex tarsalis larvae
developed faster in habitats that contained G .
ai nis . In some cases, the mosquito fi sh may
even indirectly increase the survival rate of
mosquito larvae by feeding on their cladoceran
competitors (Blaustein and Karban, 1990;
Blaustein, 1992). It has been reported that adult
mosquitoes have the ability to sense the presence
of Gambusia , and that mosquitoes reduce
oviposition rates in pools containing mosquito
fi sh (Angelon and Petranka, 2002; Van Dam

Most of the studies carried out so far have given
emphasis on the rate of consumption of
larvivorous fi sh and associated decrease in the
population of mosquitoes. However, little is
known about the ecology of many larvivorous
fi sh (Hurlbert et al ., 1972; Hurlbert and Mulla,
1981; Mef e and Snelson, 1989; Chandra et al .,
2008a) and the impacts of their introduction to
ecosystems (Hoddle, 2004). Although the
application of larvivorous fi sh is, in many cases,
a social and economic option for ef ective vector
control operations, there have been several
discouraging reports related to the application
of larvivorous fi sh.
The artifi cial introduction of Gambusia
(mosquito fi sh) into many countries beyond its
native range has af ected the natural dynamics
of ecosystems. Gambusia successfully competes
with native fi sh species and feeds on a wide
range of organisms. Mosquito fi sh, due to their
polyphagous nature, deplete the abundance of
some invertebrate taxa including predatory
insects and zooplankton. Reduction in the
abundance of predatory insects consequently
reduces the total intensity of their predation on
mosquito larvae (Bence, 1988). It facilitates
mosquito larval growth by decreasing
competitive pressure from zooplankton and
predation pressure from predatory invertebrates
(Hurlbert and Mulla, 1981; Blaustein and
Karban, 1990). Depletion in zooplankton results
in higher density of phytoplankton, which is the
principal food for larvae of many mosquito
species (Marten, 1987). Therefore, enhanced
density of phytoplankton may enhance the
density of mosquito immatures. Gambusia ai nis
can precipitate algal bloom when the fi sh feed on
zooplankton grazers (Hurlbert et al ., 1972).
Algal bloom participates in dif erent ecological
interactions with available aquatic fauna. Other
ecological changes, which occur after the
introduction of non-native larvivorous fi sh, are
increased water temperature, increased
dissolved organic phosphorus content and
decreased water clarity (Hurlbert et al ., 1972).
The indirect ef ects on non-target species by
removing their food sources can adversely af ect
native fi sh populations (Lydeard and Belk, 1993;