|
Gambusia affinis also known as mosquito fish. Copyright:
US Centers for Disease Control and Prevention
|
|
BIOLOGICAL CONTROL
Overview
Malaria
continues to kill millions of men, women and children in third world and
developing nations. The extent of this devastation is plain to see when
one looks at the world map showing where malaria exists today.
FIG. 1 Estimated incidence of
clinical malaria episodes caused by local transmission of Plasmodium
falciparum in 2004. Adapted from a map in the World Malaria
Report 2005 (WHO, 2005), with the assistance and permission of the
World Health Organization.
From: Walther and Walther (2007) Annals of Tropical
Medicine & Parasitology, 101(8): 657-672
Prevention of disease transmission by mosquitoes and other insects
requires a multifaceted approach, which includes killing mosquitoes with
pesticides and larvicides. Biological control has received less
interest over the last 3 decades, but now regaining interest because of
the resistance of mosquitoes to the chemical approach.
Biological
control may also be achieved by the use of predators that prey on
mosquito larvae in stagnant pools. The use of larvivorous fishes
(fishes that feed on larvae, such as Gambusia affinis), has been
employed successfully for many decades. However, Gambusia is an
aggressive fish that has displaced many indigenous fishes, thus causing
environmental concern in areas where they are introduced. Using
larvivorous fishes is an approach employed only in countries where
Gambusia has already been introduced or is naturally present.
Another drawback of using conventional fishes is that mosquitoes
primarily breed in stagnant bodies of water which dry up seasonally. The
introduction of Gambusia is effective only during the wet season
and will require restocking after the dry season passes and the next
rainy season sets in.
|
|
Roloffia,
a species of killifish.
Copyright
1997 Anthony C. Terceira
Nothobranchius
Copyright 1997 Jim Robinson
|
|
- Annual Killifishes
- Poseidon promotes the use
of a different larvivorous fish, called annual killifishes.
These fishes are found in freshwater and can maintain permanent
populations even in temporary bodies of water.
Adult and juvenile annual fishes die during the dry
season and reappear when the rainy season starts.
Killifishes are able to maintain stable populations because of a
unique development cycle in which the embryos laid during the wet season
can undergo a state of suspended animation, thus allowing them to survive
adverse conditions such as drought and high temperatures.
Populations of these fishes have been found in pools as small as
imprints made by elephant hooves and in areas that previously experienced
drought lasting as long as five years.
Annual killifishes feed on the larvae of mosquitoes, which also
hatch during the rainy
season. With an adequate
fish population in temporary pools, it is theoretically possible to
produce adequate biological control in special bodies of freshwater.
Besides their unique life cycle, there are advantages to
the use of annual killifishes:
·
Their small size (approximately five to seven cm.) enables
them to seek predators in shallow corners of the pool and under/in between
the leaves of water plants.
·
Their small size also makes them less suitable as a food source by
local human population that co-inhabit these areas.
·
They are rarely aggressive and have never been found to develop
populations in permanent bodies of freshwater.
·
The sturdy eggs can be mass-produced, thus making it
possible to carry millions of embryos for dissemination in difficult
terrain usually found in malarious areas.
-
Historical Perspective
- In 1952, the noted
ichthyologist, George Myers, made the first field observation that
annual fishes may have potential in biological control of mosquitoes
since mosquito bites were diminished in areas normally populated by
these fishes. It was not until two decades later in 1978 when Jonathan
Matias and Jules Markofsky, then with the Orentreich Foundation in New
York, that this idea was again re-introduced during the Columbia
University Seminars on Pollution and Water Resources. It took yet again
another two decades when Nova Pacific Research Foundation (Philippines)
received a grant from Conservation, Food and Health Foundation (Boston,
Massachusetts)
to undertake laboratory studies on the predatory activity of annual
fishes against mosquito larvae. The results of this research are
highlighted here to demonstrate the practical use of annual fish as a
biological control method.
Tests on predatory activity of annual fishes.
Table
1. The
relationship between the length, weight and larval consumption in mature
adults of annual fishes from South America and Africa. Mean and standard
Deviation of 5 fishes per test.
|
Fish Species |
Sex |
Mean ± SD |
| Length |
Weight |
Mosquito larvae consumption |
-
-
Aphyosemion gardnerii
|
Male |
4.52 ± 1 |
1.14 ± 0.16 |
50.88 ± 2.70 |
| Female |
4.40 ± 0.17 |
1.06 ± 0.18 |
44.46 ± 9.30 |
-
-
Nothobranchius melanosphilus
|
Male |
4.50 ± 0.30 |
1.23 ± 0.20 |
77.50 ± 3.06 |
| Female |
4.26 ± 0.08 |
0.80 ± 0.05 |
82.68 ± 8.87 |
-
-
Cynolebias whiteii
|
Male |
5.08 ± 0.16 |
1.10 ± 0.24 |
73.50 ± 24.7 |
| Female |
3.55 ± 0.07 |
0.45 ± 0.02 |
300.0 ± 0.0 |
-
-
Aphyosemion austriale
|
Male |
4.20 ± 0.08 |
0.55 ± 0.05 |
60.10 ± 4.63 |
| Female |
3.70 ± 0.0 |
0.40 ± 0.0 |
54.80 ± 2.24 |
- The
data in Table 1 show that different species have different rate of
consumption, with the South American species of C. whiteii showing
the highest consumption. There were no sex differences in total food
consumption, except in C. whiteii where the females showed 4 times
higher food consumption despite being half the size of the males.. These
fishes can live almost exclusively on mosquito larvae when no other food
is present. However, ponds are inhabited by many species of insect larvae
and other life forms that serve as food during the rainy season. The data
demonstrate that these fishes are predatory to mosquito larvae and may
serve as a biological control in isolated pools of fresh water.
- Figure
1. The relationship between feeding rate, weight and length in
the annual fish, Nothobranchius guentheri. Each point represents the
value for each fish in the study.
The
results for N. guentheri showed that the larger the fishes, the greater
the larval consumption rate.
Research on understanding the mechanisms that control the
onset of duration of arrested development (also known as suspended
animation or diapause) has been undertaken by Poseidon scientists for
several decades. The level of knowledge about the biology of these fishes
has reached the stage where it is now possible to mass produce annual
species for biocontrol trials. For more information about
annual fish biology please
CLICK HERE.
Poseidon’s goal is to embark on mass production of
annual killifishes to support future use of these fishes for biological
control of mosquitoes and insects. The control of suspended animation also
has major implications in studies on health, disease, and aging.
Mass production will also enable the company to support the
expansion of research in this area for possible applications in biomedical
sciences.
 Back to
Annual Fish Biology
Back to
Medical Uses
|
