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. 2020 Jul;2(7):611-620.
doi: 10.1038/s41893-019-0301-7. Epub 2019 Jul 8.

Modelled effects of prawn aquaculture on poverty alleviation and schistosomiasis control

Affiliations

Modelled effects of prawn aquaculture on poverty alleviation and schistosomiasis control

Christopher M Hoover et al. Nat Sustain. 2020 Jul.

Abstract

Recent evidence suggests that snail predators may aid efforts to control the human parasitic disease schistosomiasis by eating aquatic snail species that serve as intermediate hosts of the parasite. Potential synergies between schistosomiasis control and aquaculture of giant prawns are evaluated using an integrated bio-economic-epidemiologic model. Combinations of stocking density and aquaculture cycle length that maximize cumulative, discounted profit are identified for two prawn species in sub-Saharan Africa: the endemic, non-domesticated Macrobrachium vollenhovenii, and the non-native, domesticated Macrobrachium rosenbergii. At profit maximizing densities, both M. rosenbergii and M. vollenhovenii may substantially reduce intermediate host snail populations and aid schistosomiasis control efforts. Control strategies drawing on both prawn aquaculture to reduce intermediate host snail populations and mass drug administration to treat infected individuals are found to be superior to either strategy alone. Integrated aquaculture-based interventions can be a win-win strategy in terms of health and sustainable development in schistosomiasis endemic regions of the world.

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Conflict of interest statement

Competing interests The authors declare no competing interests

Figures

Figure 1:
Figure 1:
Model schematic representing the three components of the integrated aquaculture-epidemiologic model. Prawn aquaculture is modeled via state variables P and L. The epidemiologic model consists of the size- and age-structured snail population state variables (Nij) in grey circles and the mean worm burden in the human population, W. These two components are linked via size- and density-dependent prawn predation on snails estimated as ψij. Parameters governing transitions between snail classes and migration into and out of each class are shown: ξ is the rate of migration between the external snail population and the population at the modeled intervention site, β is the man-to-snail transmission parameter, σ is the inverse of the pre-patent period of snails, g1 and g2 are the growth rates of snails in size class 1 and 2 respectively, λ is the snail-to-man transmission parameter, and θ1 and θ2 represent increased contribution of larger snails to human infection.
Figure 2:
Figure 2:
Prawn aquaculture model dynamics. Two-year aquaculture cycles for M. rosenbergii (red lines) and M. vollenhovenii (blue lines) under optimal management showing how prawns grow in length over time (bottom-left), but decrease in density (top-left). This leads to a single peak in harvest mass (top-right), but harvesting actually occurs prior to the peak in order to maximize ten-year cumulative profits (bottom-right) by sacrificing profit-per-cycle for completing more aquaculture cycles. Vertical dashed lines indicate time at which harvest would occur for each species (small dashes – M. rosenbergii, large dashes – M. vollenhovenii). Harvest of the slower-growing M. vollenhovenii occurs later as they take longer to grow in size and biomass. Here, following, the cost c for a juvenile prawn is 0ドル.10 with L0 = 40mm (~0.35g per juvenile prawns) and the selling price is p=$12/kg. Other parameters set as in Table 1.
Figure 3:
Figure 3:
Grid search to identify optimal management decisions for each prawn species. Cumulative profits (CPsp) generated by the aquaculture model for each species across a range of potential stocking densities (P0) and harvest times (T) are shown. Grey regions indicate regions where harvesting is not feasible due to prawns not having reached sufficient marketable size (30g) due to insufficient time to grow and density-dependent growth rates. Contours indicate regions of CPsp corresponding to the labeled value in 2018 USD.
Figure 4:
Figure 4:
Outputs of the integrated model under different intervention scenarios implemented over ten years followed by ten years of no intervention. Worm burden trajectories under no intervention (red), annual MDA only (purple), prawn stocking of M. rosenbergii under optimal management (blue), and both annual MDA and prawn stocking (gold) (A); snail infection dynamics under MDA-only intervention (B); and snail infection dynamics under prawn stocking interventions (C). Outputs from M. volenhovenii interventions not shown as they approximately mirror those of M. rosenbergii since the profit-maximizing stocking densities of both species result in maximal reductions in the snail population.

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