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Keywords:

  • dengue;
  • Aedes aegypti;
  • biological control;
  • larvivorous fish;
  • Betta splendens

Summary

  1. Top of page
  2. SummaryLa survie des poissons Betta splendens (Regan, 1910) dans des conteneurs d’eau domestiques et leur efficacité dans la lutte contre les larves d’Aedes aegypti (Linneaus, 1762) dans le nord-est du BrésilSupervivencia de los peces Betta splendens (Regan, 1910) en contenedores de aguas domésticas y su efectividad para el control de larvas de Aedes aegypti larvae (Linnaeus, 1762) en el noreste de Brasil
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Objective  In Northeast Brazil, large domestic containers used to store water are important breeding sites of Aedes aegypti, the main vector of dengue fever. The objective of this study was to estimate the survival of Betta splendens (Perciformes: Osphronemidae) fish in domestic containers in Fortaleza (Ceará State), as well as its effectiveness in the control of premature A. aegypti stages.

Methods  The use of B. splendens was compared to Bacillus thuringiensis israelensis (Bti) in domestic containers. In a first home visit, B. splendens or Bti were applied to water containers. Two follow-up visits were conducted after 3–4 and 5–6 months to assess the presence of viable fish in the containers and infestation by larvae. Betta splendens fish were still present in 97.6% of containers 45–60 days after application. When the fish was present, the infestation rate was significantly higher (< 0.001) in the Bti group (IR ratio = 21.60; 95% CI: 6.46–72.28). In deposits where the fish remained, efficacy was 85% better than Bti. The permanence of fish was higher in concrete tanks (48.5%) located outside the house (47.5%) and at ground level (53.3%). We conclude that B. splendens may be suitable for biological control of A. aegypti larvae in large domestic water containers, but that appropriate measures should be taken to assure prolonged survival and the presence of fish in the containers.

La survie des poissons Betta splendens (Regan, 1910) dans des conteneurs d’eau domestiques et leur efficacité dans la lutte contre les larves d’Aedes aegypti (Linneaus, 1762) dans le nord-est du Brésil

Objectif:  Dans le nord du Brésil, de grands conteneurs à usage domestique utilisés pour stocker l’eau sont d’importants sites de reproduction du moustique Aedes aegypti, principal vecteur de la dengue. L’objectif de cette étude était d’estimer la survie des poissons Betta splendens (Perciformes: Osphronemidae) dans les conteneurs à usage domestique à Fortaleza (Etat du Ceará), ainsi que leur efficacité dans la lutte contre les stades pré matures d’A. aegypti.

Méthodes:  L’utilisation de B. splendens a été comparée à celle de Bacillus thuringiensis israelensis (Bti) dans des récipients domestiques. Dans une première visite à domicile, B. splendens ou Bti a été introduit dans les réservoirs d’eau. Deux visites de suivi ont été effectuées au bout de 3-4 et 5-6 mois pour évaluer la présence de poissons viables dans les conteneurs et les infestations par les larves. Les poissons B. splendensétaient encore présents dans 97,6% des conteneurs 45-60 jours après l’introduction. Lorsque le poisson est présent, le taux d’infestation était significativement plus élevé (p <0,001) dans le groupe de Bti (IR ratio = 21,60; IC95%: 6,46 à 72,28). Dans les dépôts où le poisson a persisté, l’efficacitéétait 85% meilleure qu’avec Bti. La persistance des poissons était élevée dans les cuves béton (48,5%), situées à l’extérieur des maisons (47,5%) et au niveau du sol (53,3%). Nous concluons que B. splendens peut être adapté pour la lutte biologique contre les larves d’A. aegypti dans de grands conteneurs d’eau domestiques, mais que des mesures appropriées devraient être prises pour assurer la présence et la survie prolongée des poissons dans les conteneurs.

Mots-clés:  dengue, Aedes aegypti, lutte biologique, poissons larvivores, Betta splendens.

Supervivencia de los peces Betta splendens (Regan, 1910) en contenedores de aguas domésticas y su efectividad para el control de larvas de Aedes aegypti larvae (Linnaeus, 1762) en el noreste de Brasil

Objetivo:  En el nordeste de Brasil, los grandes contenedores domésticos utilizados para el almacenaje agua son importantes criaderos de Aedes aegypti, el principal vector de la fiebre del dengue. El objetivo de este estudio era estimar la supervivencia de peces Betta splendens (Perciformes: Osphronemidae) en contenedores domésticos en Fortaleza (Ceará State), así como su efectividad en el control de estadios más tempranos de A. aegypti.

Métodos:  Se comparó el uso de B.splendens con Bacillus thuringiensis israelensis (Bti) en contenedores domésticos. En una primera visita a los hogares, se depositaron B.splendens o Bti en los contenedores de agua. Se realizaron dos visitas de seguimiento después de 4 y 5-6 meses para evaluar la presencia de peces viables en los contenedores y el nivel de infestación de larvas. Los peces Betta splendens aún estaban presentes en un 97.6% de los contenedores 45-60 días después de haber sido depositados. Cuando los peces estaban presentes, la tasa de infestación era significativamente más alta (p<0.001) en el Grupo Bti (IR ratio=21.60; 95% IC:6.46–72.28). En depósitos en donde los peces permanecían, la eficacia era de un 85% más que con Bti. La permanencia de los peces era mayor en tanques concretos (48.5%) localizados fuera de las casas (47.5%) y a nivel del suelo (53.3%).

Conclusiones: B. splendens puede ser un buen control biológico de larvas de A. aegypti en grandes contenedores de agua, pero son necesarias unas medidas apropiadas que aseguren la supervivencia prolongada y la presencia de los peces en los contenedores.

Palabras clave:  Dengue; Aedes aegypti; control biológico; peces larvívoros; Betta splendens.


Introduction

  1. Top of page
  2. SummaryLa survie des poissons Betta splendens (Regan, 1910) dans des conteneurs d’eau domestiques et leur efficacité dans la lutte contre les larves d’Aedes aegypti (Linneaus, 1762) dans le nord-est du BrésilSupervivencia de los peces Betta splendens (Regan, 1910) en contenedores de aguas domésticas y su efectividad para el control de larvas de Aedes aegypti larvae (Linnaeus, 1762) en el noreste de Brasil
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Larvivorous fish have been used to control various insect vectors, such as malaria vectors in natural breeding sites (Molloy 1924; Rojas et al. 2004). For example, the fish Poecilia reticulata has been successfully used in the control of the mosquitoes Culex quinquefasciatus and Anopheles gambiae in rivers and lakes in Cuba, Sri Lanka and French Polynesia (Koldenkova et al. 1989; Garcia et al. 1991; Lardeux et al. 2002; Kusumawathie et al. 2008). Less frequently, biological control of vector mosquitoes using larvivorous fish has been performed in domestic breeding sites. Gambusia affinis, Aphanius dispar and Oreochromis niloticus were used successfully in ground tanks and wells to control Anopheles funestus and C. quinquefasciatus in India, Ethiopia and Kenya (Dixit et al. 1981; Fletcher et al. 1992; Sharma et al. 1997; Howard et al. 2007).

The fish Betta splendens Regan (Perciformes: Osphronemidae) (the Siamese fighting fish) has biological characteristics that favour its use in the control of Aedes aegypti larvae in domestic containers: a high larvae-eating capacity, and the capacity to survive for a prolonged time in chlorinated water. In containers with 2 l of water, they were capable of killing an average of 319 Anopheles stephensi pupae in a single day (Gosh et al. 2004). After 5 weeks of continuous exposure to A. aegypti larvae in laboratory conditions, female B. splendens were able to eat up to 500 third stage larvae per day (Pamplona et al. 2007). Specimens of B. splendens survived at 1.0 mg/l concentration of chlorine with no apparent discomfort and 75% of them survived at concentrations of 1.50 mg/l (Cavalcanti et al. 2009). In Brazil, residual concentrations of chlorine in domestic containers range from 0.50 to 2.00 mg/l (Brasil, 2004). However, the permanence of this fish species in domestic containers with chlorinated water under field conditions has not yet been described.

The Brazilian dengue control programme is based on the reduction in breeding sites and the control of immature and adult vectors of A. aegypti (Brasil, 2009). Breeding sites are reduced by the community that is mobilized through education activities aimed at families and the population in endemic areas. The control of immature and adult forms insect of A. aegypti is carried out by control agents. They place larvicides in potential domestic breeding sites at regular intervals. In addition, insecticide is applied at ultralow volume to target adult mosquitoes. In the city of Fortaleza, when this study was developed, immature forms of A. aegypti were controlled through the application of the larvicide Bti in all potential breeding sites, every 2 months, throughout the year (Brasil, 2009). At that time, there were approximately 800 000 residences in the city of Fortaleza and the Programme had more than 1000 health agents developing education activities to reduce breeding sites and control the immature forms A. aegypti. These activities, with this frequency and coverage, have been developed in the city of Fortaleza since 2001 (Municipal Health Coordinator, personal communication). Despite these great control efforts, in 2003, there was a large outbreak of dengue fever with 9012 cases and 169 haemorrhagic cases (Cavalcanti et al. 2010).

Preliminary results showed that one specimen of B. splendens can eat about 500 A. aegypti larvae per day (Annual Meeting of Brazilian Society of Tropical Medicine, 2001). Afterwards, a local newspaper reported that the ‘Betta’ was very efficacious as a predator of Aaegypti larvae. As a result, the population started placing specimens of Betta fish in domestic containers on their own. In the city of Fortaleza, the fish can be purchased in shops selling ornamental fishes for aquariums. In addition, they can be fished in local lakes on the outskirts of the city (Pamplona 2006). In Northeast Brazil, the A. aegypti Control Programme of the municipality of Fortaleza, the capital of Ceará State, has used B. splendens fish in domestic containers as a biological control strategy of A. aegypti since 2001.1 The municipal Dengue Control Programme adopted this procedure as a control strategy, and in 2002, there were approximately 200 000 residential containers with Betta fish in Fortaleza (Oliveira-Lima et al. 2003).

In the Northeast Brazil, especially in areas where the public water supply is intermittent, the population uses containers to accumulate water. This has been a major obstacle for the control of A. aegypti, in addition to the economical impact by consuming large amount of larvicides (Brasil, 2009). People use ground tanks because in some areas the water pressure provided by the public water supply is not enough to reach elevated tanks. Moreover, it is not possible to put permanent covers on ground tanks because the water is taken trough the tank mouth. So, B. splendens fish is particularly suitable to be use in ground tanks. The objective of the this study was to estimate the duration of time B. splendens fish survive in domestic containers under field conditions and to assess the effectiveness in the control of A. aegypti larvae compared to the biopesticide Bacillus thuringiensis var. israelensis (Bti).

Methods

  1. Top of page
  2. SummaryLa survie des poissons Betta splendens (Regan, 1910) dans des conteneurs d’eau domestiques et leur efficacité dans la lutte contre les larves d’Aedes aegypti (Linneaus, 1762) dans le nord-est du BrésilSupervivencia de los peces Betta splendens (Regan, 1910) en contenedores de aguas domésticas y su efectividad para el control de larvas de Aedes aegypti larvae (Linnaeus, 1762) en el noreste de Brasil
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Study location

The city of Fortaleza is the capital of Ceará State in Northeast Brazil. It has a population of about 2.5 million and is located in the tropics, with an average temperature between 26 and 27 °C and a relative humidity of 81 ± 7%. The study was performed in the neighbourhood ‘Serviluz’ in Fortaleza. This community suffers frequent water supply outages, with the consequence that the population uses a variety of receptacles and containers for water storage. At the time of the study, Brazil’s National Dengue Control Programme (PNCD) recommended the use of the larvicide Bacillus thuringiensis israelensis (Bti). Granular formulation (Abbott Laboratórios do Brasil Ltda, IL, USA) was used and applied following indications of the PNCD (0.02 g/l) in all types of domestic water containers that cannot be eliminated every 60 days, which would mean six treatment cycles per year (Brasil, 2009). In 2001, Fortaleza’s Dengue Control Programme (PMCD) introduced in addition the use of B. splendens fish for the control of immature forms of A. aegypti in water containers with a volume >200 l.

Study design and data collection

We used data collected by PMCD agents during routine field activities from October 2002 to April 2003. The Control Programme had a record, for every water container in the household, about the type of treatment (Fish or Bti) used in the previous cycle of treatment. Based on this information, containers were classified as Fish group or Bti group. On the first house study visit, containers from the Fish group were treated with a new specimen of B. splendens fish: a new specimen was placed if no fish was present in the container, or a specimen present in the container was replaced by a new one. Accordingly, the containers from the Bti group were treated with Bti at the first study visit. Subsequently, there were two follow-up visits, the first during the third or the forth month and the second between the fifth and sixth month of observation. During these visits, the presence of viable fish in the containers was checked and infestation status by immature forms of A. aegypti larvae assessed. The observation of the water container stopped when: (i) immature forms of A. aegypti were observed in the container; (ii) the Betta fish was absent; (iii) the study period had finished (censoring time).

Characteristics of the containers

During the first visit, information about the containers was recorded regarding its type (elevated tanks or ground tanks), material (brick or cement, concrete, asbestos, plastic, metal or fibreglass), location (inside or outside the house), volume (calculated using the dimensions of the container), height above the ground and the presence of cover.

Assessment of infestation

Infestation of the containers was determined by the presence of immature forms of A. aegypti. The containers were inspected using a torch, and all immature forms were removed using a sweep net, placed in glass test tubes containing 75% alcohol and taken to the laboratory, where the immature A. aegypti were identified and counted.

Statistical analysis

To calculate the infestation rate, the observation time was the period between the first visit and the date on which the immature forms of A. aegypti were observed, or the period between the first visit and the date of the last visit (censoring time) for those containers that never were infested. To calculate the permanence rate of the fish in the containers, the observation time was the period between the first visit and the date on which the absence of fish was observed, or the period from the first visit to the date of the last visit (censoring time) for those containers in which fish were present during all the visits. The probability of the permanence of B. splendens in the containers over time was estimated by the life table method. Permanence rate was calculated by dividing the number of containers with fish present by the sum of the observation time for the containers. Similarly, the infestation rate of containers was calculated by dividing the number of infested containers by the sum of the observation time for the containers. The association between containers’ characteristics and permanence of fish or infestation, as well as the association between containers’ characteristics and treatment (Bti or Fish) was assessed by means of permanence rate ratio and infestation rate ratio and its 95% confidence intervals, calculated through Poisson regression. Characteristics associated with infestation, in a multivariate model, with a P value ≤0.250 were considered confounders and were included in a final multivariate Poisson regression model to assess the relationship between treatment and infestation (Hosmer & Lemeshow 2000).

Results

  1. Top of page
  2. SummaryLa survie des poissons Betta splendens (Regan, 1910) dans des conteneurs d’eau domestiques et leur efficacité dans la lutte contre les larves d’Aedes aegypti (Linneaus, 1762) dans le nord-est du BrésilSupervivencia de los peces Betta splendens (Regan, 1910) en contenedores de aguas domésticas y su efectividad para el control de larvas de Aedes aegypti larvae (Linnaeus, 1762) en el noreste de Brasil
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

In total, 1001 houses were inspected, and 974 large volume containers identified (>200 l). Five hundred and thirty-seven (55.1%) containers belonged to the B. splendens group and 437 (44.9%) to the Bti group. Initially, the duration of the presence of B. splendens in domestic water containers was estimated (Table 1). A high proportion (97.6%) was present at 45–60 days, and then this proportion dropped rapidly. In one container, the fish remained for at least 183 days.

Table 1.   Permanence of Betta splendens in domestic containers with water (N = 537), according to the observation time
Time of observation (days)TotalContainers with fishCensored containersProportion of containers with fish (95% CI)
45–60537131097.6% (95.8–98.6)
61–8951416311762.7% (58.1–66.9)
90–1832341518313.5% (10.0–17.5)

The characteristics of containers associated with the duration of the presence of the fish specimens were assessed (Table 2). The permanence rate was significantly longer in ground tanks (< 0.001), in brick and cement or concrete tanks (= 0.018), in containers situated outside the house (= 0.038) and in those located <1 m above the ground (= 0.002). The volume of the container and the presence of a cover were not significantly associated with the permanence of the fish. In the multivariate analysis, only the type of container remained significantly associated with the permanence of fish (adjusted incidence rate ratio = 1.99; 95% CI: 1.41–2.83; < 0.001).

Table 2.   Permanence of Betta splendens in domestic water containers (N = 537), according to the features of the deposits
Characteristics of depositsIncidence rate (IR)IR ratio (95% CI)P
Time (days)N° of presenceIR
  1. *The first category was the reference category.

Type of container
Elevated tank20017 8495229.131.81 (1.32–2.47)<0.001
Ground tank33730 01615852.64
Construction material
Other15413 8214532.561.49 (1.07–2.07)0.018
Brick/concrete38334 04416548.47
Localization
Indoors13111 8643932.871.44 (1.02–2.05)0.038
Peridomestic40636 00117147.49
Volume in litres
200–200046441 35817742.791.19 (0.82–1.72)0.371
2001–10 0007365073350.71
Height in metres
<126924 01112853.310.65 (0.49–0.85)0.002
1.1–926823 8548234.38
Presence of cover
No19917 6558045.310.95 (0.72–1.25)0.716
Yes33830 21013043.03
Multivariate model*
Type of container1.99 (1.41–2.83)<0.001
Material1.35 (0.95–1.91)0.098
Localization1.37 (0.96–1.96)0.079
Volume1.47 (0.96–2.24)0.073
Cover1.08 (0.80–1.46)0.609

Factors associated with container infestation by A. aegypti larvae were investigated to identify the potential confounders of the relationship between treatment and infestation (Table 3). The incidence rate of infestation by Aedes larvae was significantly higher in ground tanks (< 0.001), in brick and cement/concrete containers (= 0.008), in containers with a volume <2000 l (= 0.013), in containers <1 m above the ground (< 0.001) and in uncovered containers (< 0.001). Infestation was not significantly associated with the location of the container. After adjustment, only the type of container was significantly (< 0.001) associated with infestation. The infestation rate was 2.74; 95% CI: 1.58–4.76 times longer in ground tanks than in elevated tanks. To understand how a containers’ characteristics work as confounders, the association between containers’ characteristics and treatment was assessed (data not shown in tables). Type of deposits, material and the presence of cover were significantly associated with treatment group. Among containers from the Fish group, there was a higher proportion of ground tanks (< 0.001), brick and cement/concrete containers (< 0.001) and uncovered containers (< 0.001). To estimate the relationship between treatment and infestation, not adjusted and adjusted to confounders, a multivariate analysis was performed by means of Poisson regression models (Table 4). In non-adjusted analysis, when the fish was present, the infestation rate was significantly higher (= 0.001) in the Bti group [infestation rate (IR) ratio = 6.72; 95% CI: 2.08–21.64]. However, when the fish was not present in the container, the infestation rate was significantly lower (< 0.001) in the Bti group (IR ratio = 0.39; 95%; CI: 0.27–0.57). Different results were obtained in the multivariate analysis. When the fish was present, the infestation rate was significantly higher (< 0.001) in the Bti group (IR ratio = 21.60; 95% CI: 6.46–72.28). In deposits where the fish remained, efficacy was 85% better than Bti. But when the fish was absent, the incidence rate was similar in both groups (= 0.471).

Table 3.   Infestation rate of all domestic containers (Fish and Bti groups combined; N = 974) with immature forms of Aedes aegypti, according to container characteristics
CharacteristicsInfestation rate (IR)IR ratio (95% CI)P
TimeInfested containersIR
  1. *The first category was the reference category.

Type of container
Elevated tank58852 734407.593.37 (2.32–4.89)<0.001
Ground tank38634 4148825.57
Construction material
Other32629 471299.841.74 (1.15–2.64)0.008
Brick/concrete64857 6779917.16
Localization
Indoors22219 3782613.411.12 (0.73–1.73)0.601
Peridomestic75267 77010215.05
Volume in litres
200–200080271 42011616.240.47 (0.26–0.85)0.013
2001–10 00017215 728127.63
Height in metres
<130827 5236824.710.41 (0.29–0.58)<0.001
1.1–966659 6256010.06
Presence of cover
No29225 9146023.150.48 (0.34–0.68)<0.001
Yes68261 2346811.10
Multivariate analysis*
Type of container2.74 (1.58–4.76)<0.001
Material1.45 (0.92–2.26)0.106
Volume0.67 (0.35–1.29)0.322
Height1.03 (0.63–1.68)0.907
Presence of cover0.72 (0.49–1.05)0.089
Table 4.   Infestation rate of Aedes aegypti in domestic containers with water, according to the group (Betta splendens or Bti), adjusted or not to potential confounders
Type of analysisInfestation rate (IR)IR ratio (95% CI)P
Time (days)Infested containersIR 10.000
  1. *Only the reservoirs from the ‘fish group’ with fish at the moment of infestation ascertainment.

  2. †Only the reservoirs from the ‘fish group’ without fish at the moment of infestation ascertainment.

  3. ‡IR ratio adjusted for ‘type of reservoir’, ‘material’ and ‘cover’.

Not adjusted
 Fish present*21018 40531.6310.001
6.72
(2.08–21.64)
 Bti43739 2834310.94  
Not adjusted
 Fish absent†32729 4608227.831<0.001
0.39
(0.27–0.57)
 Bti43739 2834310.94  
Adjusted
 Fish present*1<0.001
21.60‡
(6.46–72.28)
 Bti  
Adjusted
 Fish absent†10.471
0.85‡
(0.56–1.31)
 Bti  

Discussion

  1. Top of page
  2. SummaryLa survie des poissons Betta splendens (Regan, 1910) dans des conteneurs d’eau domestiques et leur efficacité dans la lutte contre les larves d’Aedes aegypti (Linneaus, 1762) dans le nord-est du BrésilSupervivencia de los peces Betta splendens (Regan, 1910) en contenedores de aguas domésticas y su efectividad para el control de larvas de Aedes aegypti larvae (Linnaeus, 1762) en el noreste de Brasil
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Our study suggests that B. splendens is more effective than the larvicide Bacillus thuringiensis israelensis (Bti) as a control method of immature forms of A. aegypti. When the fish was present in a container, the incidence of immature forms of A. aegypti was 19 times lower than in containers treated with Bti. This is the first investigation of the effectiveness of B. splendens as a control strategy of immature forms of A. aegypti in domestic water containers (Pamplona 2006). This study only considered containers with a volume equal or larger than 200 l, such as ground tanks and elevated tanks and drums. In Fortaleza, these big water containers are essential to store water because the public water supply usually only reaches households for a few hours each day (Caprara et al. 2009).

The use of Betta fish to control the immature forms of A. aegypti in large volume containers may have a great impact on transmission, as these containers are responsible for a big proportion of pupae (Pamplona et al. 2004; Romero-Vivas et al. 2006; Koenraadt et al. 2007). On the other hand, these large volume containers consume the biggest amounts of larvicides. According to the Brazilian Ministry of Health, in the State of Ceará alone, in 2009, US$ 4.5 million was spent on larvicides for A. aegypti control (Brasil, 2009). This cost would be reduced if the larvicide was substituted by fish (Bheema et al. 1982; Neng et al. 1987; Conejo et al. 2000; Martinez-Ibara et al. 2002; Mohamed 2003).

As the selection of the type of container to receive fish or be treated with Bti was not random, this result could be confounded if factors facilitating the infestation of containers with A. aegypti were positively associated with the containers treated with Bti. However, the opposite occurred. The fish group had a significantly higher proportion of ground tanks, brick and cement/concrete containers and uncovered containers (data not shown in table). These categories of the respective variables were associated with the highest infestation rate of A. aegypti (Table 2). As expected, the adjusted odds ratio (OR = 19.69) of infestation was much higher than the unadjusted one (OR = 6.72). Up to 60 days, only 2.4% of the containers were observed without any fish. However, this proportion increased to 37.4% at the end of the third month. Thus, in the routine of the control programme, after 60 days, all containers that received fish should be examined to replace any absent fish. Sixty days are also the critical point for the residual effects of the Bti. In an experimental study with renewed water, to simulate the conditions in a domestic water container, only 38–44% of A. aegypti larvae died 60 days after the water was treated with Bti larvicide (Pontes et al. 2005, 2010).

The water in domestic water containers has some characteristics which may influence the longevity of Betta fish, such as the level of nutrients and the chlorine concentration. Assuming that the water for domestic consumption has a lower concentration of organic matter than natural breeding sites, it is probable that this restriction of nutrients is a factor reducing the longevity of Betta fish in domestic water containers. Regarding chlorine, it has been demonstrated that 27.5% of the fish specimens do not resist concentrations of chlorine of 1.5 mg/l (Cavalcanti et al. 2009). In Fortaleza, the concentration of chlorine in the public water supply varies between 0.55 and 1.83 mg/l (Companhia de água e esgoto do Ceará (CAGECE), 2007).

The influence of certain characteristics of containers (type, material, location, volume, height and the presence of a cover) on the longevity of Betta fish was investigated. In particular, the volume of the container may influence the survival of the Betta because this species has the habit of being in constant movement (Bronstein 1994), and consequently, in large containers they would consume more energy, leading to a greater possibility of death because of energy exhaustion. However, in our study, no significant relationship was observed between the volume of the container and the longevity of the fish. During the study’s 6 month observation, the incidence rate of Betta fish was 1.99 times higher in the ground tanks than the elevated tanks, after adjustment for other characteristics of the containers. This result has great practical importance because it is easier to monitor the presence of fish in ground tanks than in elevated tanks.

In this analysis, the presence of the Betta fish in a container at any time was used as an indicator of the fish’s survival until that point. When absent, the fish was considered dead. However, a fish may be absent because it left the container through the overflow pipe or when the container overflowed. Putting a mesh over the pipe would prevent the escape of fish while preventing the overflow of water. Monitoring the fish’s presence should be continuous and might be costly and inefficient if performed by the Control Programme agents. Hence, the monitoring should be performed by the community, who would report the absence of fish to the Control Programme, which would take the necessary measures. Community participation in integrated vector control programmes has produced good results and cost reductions (Neng et al. 1987; Martinez-Ibara et al. 2002).

Footnotes

Acknowledgements

  1. Top of page
  2. SummaryLa survie des poissons Betta splendens (Regan, 1910) dans des conteneurs d’eau domestiques et leur efficacité dans la lutte contre les larves d’Aedes aegypti (Linneaus, 1762) dans le nord-est du BrésilSupervivencia de los peces Betta splendens (Regan, 1910) en contenedores de aguas domésticas y su efectividad para el control de larvas de Aedes aegypti larvae (Linnaeus, 1762) en el noreste de Brasil
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

We thank the technicians Roberto Varela, Socorro Furtado and Carlos Alberto for supervision of the fieldwork and the endemic agents of Fortaleza for their important contributions to field activities. J.H. is a research fellow from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq/Brazil).

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  1. Top of page
  2. SummaryLa survie des poissons Betta splendens (Regan, 1910) dans des conteneurs d’eau domestiques et leur efficacité dans la lutte contre les larves d’Aedes aegypti (Linneaus, 1762) dans le nord-est du BrésilSupervivencia de los peces Betta splendens (Regan, 1910) en contenedores de aguas domésticas y su efectividad para el control de larvas de Aedes aegypti larvae (Linnaeus, 1762) en el noreste de Brasil
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
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