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# The application of Global Burden of Animal Diseases methodology to aquatic animal production

E.J. Peeler* (1,2), E. Brun (3), B. Misund (4), W. Gilbert (2), B. Huntington (2, 5), M. Reantaso (6), C. Walde (3) & A. Kennerley (1)

(1) Epidemiology and Risk Group, Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, Weymouth, DT4 8UB, United Kingdom

(2) Department of Livestock and One Health, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, 146 Brownlow Hill, Liverpool, L3 5RF, United Kingdom

(3) Fish Health and Fish Welfare, Norwegian Veterinary Institute, PB 64, N-1431 Ås, Norway

(4) Department of Economics and Finance, University of Stavanger, Business School, PO Box 8600, N-4036 Stavanger, Norway

(5) Pengwern Animal Health Ltd, 259 Wallasey Village, Wallasey Wirral, Merseyside, CH45 3LR, United Kingdom

(6) Fisheries and Aquaculture Division, Food and Agriculture Organization of the United Nations, Viale delle Terme di Caracalla, 00153 Rome, Italy

*Corresponding author: ed.peeler@cefas.gov.uk

## Summary

The Global Burden of Animal Diseases (GBADs) programme's key objective – to provide a systematic approach to determine the burden of animal disease – is as relevant to aquatic as to terrestrial animal production systems. However, to date GBADs methods have mainly been applied to terrestrial animal production systems. The challenges in applying GBADs methods, notably the Animal Health Loss Envelope (AHLE), vary considerably by production system. The authors demonstrate how the AHLE can be calculated for rainbow trout production in England and Wales and acknowledge that its application to other systems (e.g. hatchery production, polyculture and no-feed mollusc production) is more complex. For example, in small scale tropical fish production the impact of suboptimal nutrition on production would need to be addressed. Recirculating aquaculture systems have inherent high levels of biosecurity and disease control, and thus low levels of disease. Removing the capital and running costs associated with biosecurity fundamentally changes the system and invalidates the AHLE calculation. Lack of data from many systems, notably small-scale tropical finfish farming, means that expert opinion will be needed to support the application of GBADs methods. While calculation of the AHLE is the focus of this article, it should be noted that attribution to causes and value chain modelling are needed to generate data on the wider societal impact of aquatic animal diseases (and possible interventions), which governments require to support decision-making about resource allocation.

## Keywords

Animal health – Animal Health Loss Envelope – Aquaculture – Disease burden – Economics – GBADs – Global Burden of Animal Diseases – Shrimp – Trout.

## Introduction

Aquaculture has been practised for many centuries, but it was only in the 19th century that intensive breeding and production started with brown trout (*Salmo trutta*), initially to supplement wild populations diminished by pollution and obstructions to migration. In the 1950s, the development of artificial pelleted feed allowed for the rapid expansion of freshwater rainbow trout (*Oncorhynchus mykiss*)

production for human consumption. In the 1970s, the development of inexpensive, light, robust floating cages led to Atlantic salmon (*Salmo salar*) production in the marine environment, which grew rapidly in Europe (Norway and Scotland) and Chile. Technological developments resulted in a similarly rapid expansion of penaeid shrimp farming, predominantly in Asia, from the 1980s. Aquaculture now contributes more to the global food supply than wild capture fisheries [1].
The expansion and intensification of aquaculture, accompanied by the emergence and spread of diseases that had serious economic impacts to the industry and environmental impacts (e.g. biodiversity loss) [2,3], stimulated the application of epidemiology to aquatic production. Epidemiological approaches developed in the human and terrestrial animal fields were first applied to aquatic animal diseases in the late 1980s (reviewed by Peeler and Taylor [4]). There now exists an extensive body of published epidemiological studies of aquatic animal diseases. However, most research has focused on commercial salmonid and shrimp production, with few studies investigating production and disease in smaller-scale, subsistence aquaculture. Similarly, information on the cost of aquatic animal diseases is available mainly for disease outbreaks in salmonid and shrimp production. Very few studies have examined costs of disease at a production-system or national level. Moreover, there is a lack of information about expenditure on disease prevention and control, which should be examined alongside losses to achieve a holistic view of the burden [5]. Control of internationally listed transboundary and epidemic diseases has, arguably, driven government decisions about and resource allocation to aquatic animal health, at the expense of control of endemic diseases [6]. Similar observations have been made regarding funding of epidemic and endemic human disease [7]. The lack of information on the true cost of endemic aquatic animal disease may be partly to blame for its neglect.

The Global Burden of Animal Diseases (GBADs) programme seeks to address the deficiency in information on the losses attributable to animal disease and health expenditure. The programme includes aquatic animals in its scope, and it has become incorporated as a pillar in the Food and Agriculture Organization of the United Nations (FAO) progressive management pathway for aquatic biossecurity [8]. Under the auspices of FAO, a technical working group was convened in April 2021 to support developing a framework for understanding the burden of diseases of farmed aquatic organisms [9]. The working group identified the key considerations when applying the GBADs framework to aquaculture (summarised in Box 1). This led to short-duration scoping projects in Vietnam and Ghana to better understand the aquatic animal data ecosystem and how the political landscape impacts decision-making related to aquatic animal health. The extent to which GBADs methods have been applied to aquatic animal production is, therefore, limited. This article a) assesses the challenges of applying GBADs methods across a number of diverse aquatic animal production systems (grow-out, hatchery, mollusc and recirculation systems), b) uses GBADs methods to calculate the burden of disease in a typical rainbow trout farm in England and c) considers how analyses using GBADs methods may address shortcomings in the current literature.

## Box 1

### Challenges and considerations when applying the Global Burden of Animal Diseases framework to aquaculture

- Both public and private decision-makers rely on economic evaluation to make strategic, operational and contingency decisions related to aquaculture.

- The management of water is central to the structure and operation of aquaculture systems, the epidemiology of diseases, prevention and control measures, and therefore investment, losses and costs of diseases.

- Aquaculture systems are highly diverse, with small producers being very important for most farmed species. Sufficient variables to classify aquaculture production systems are species, production phase, type of production (one or two variables), intensification and size.

- The structure of disease losses is similar to that for terrestrial animals. Co-infection of diseases makes it difficult to establish the impact of a specific disease. Water connectivity makes it more difficult at the aggregate level for many systems (compared with terrestrial production) to establish epidemiological boundaries between production units.

- A complexity of many aquaculture systems is the difficulty of monitoring individuals due to population size and poor accessibility and visibility, increasing under-reporting or misclassification of disease.

- The expenses of diseases derive from prevention and control, and escalate significantly in emergency situations. Expense categories are similar to those established for terrestrial animals.

- In aquaculture, environmental emergencies can have important impacts on production that can impose costs from both prevention and response, similar to infectious diseases.

- Large companies and governments of developed countries hold most of the data.

- Elsewhere (e.g. small-scale production in developing countries) data are more limited.

Source: adapted from Rojas et al. [9]

### Application of Global Burden of Animal Diseases methods to aquatic animal production

The GBADs programme provides data-driven evidence that policy-makers can use to evaluate options, inform decisions, and measure the success of animal health and welfare interventions. The programme will glean existing data to measure animal health losses within carefully characterised production systems. Consistent and transparent attribution of animal health losses will enable meaningful comparisons of the animal disease burden to be made between diseases,
production systems and countries, and will show how this burden is apportioned by people's socio-economic status and gender. The GBADs programme will produce a cloud-based knowledge engine and data portal through which users will access burden metrics and associated visualisations, support for decision-making in the form of future animal health scenarios, and the outputs of wider economic modelling.

## Drivers

The key driver for developing the GBADs programme is the lack of a systematic process to determine the burden of animal disease. The programme seeks to address the lack of systematic collection of data for a) production losses, b) expenditure on disease control and c) the wider economic impact of disease, and thus support decision-making and ultimately improve societal outcomes from animal production. These objectives are equally relevant to aquatic as to terrestrial animal production. The methods can be applied at the production-system, country and global levels.

## The range of aquaculture production systems

Today, over 500 aquatic species, among them finfish, molluscs, crustaceans and aquatic plants, are being cultivated across the globe in diverse habitats. Countries engaged in aquaculture vary from low-income to high-income nations. The scale of production ranges from high to low intensification and expansion, and access to and utilisation of technology, in

addition to data recording and accessibility, further contribute to the large diversity within aquaculture production. All these factors create challenges to applying GBADs methods. These challenges vary greatly between production systems, which can be classified using a number of factors [9,10]:

- inputs (intensity) (feed, disease control, energy; stocking density, capital);

- species (finfish, molluscs, crustaceans);

- scale (large, medium, small);

- feed (fed versus non-fed, pasteurised versus unpasteurised);

- production input (hatchery, wild stock);

- environment (freshwater, brackish, marine; land-based versus water-based);

- polyculture versus monoculture;

- integrated (e.g. livestock-fish) versus unintegrated;

- commercialisation/ownership (production for subsistence, local or national markets, or export).

From a GBADs perspective, and notably for the calculation of the Animal Health Loss Envelope (AHLE), classifying aquaculture production systems by inputs is informative. In Table I, selected aquatic animal production systems are assessed by level and type of input. Local definitions of production system classification may be necessary when assessing the construction of local datasets. Therefore, a flexible system that respects both local understanding and aggregation to generate burdens at national and global levels is needed.

<caption>Table I</caption>

Aquaculture production systems classified by the intensity of inputs

<table><thead><tr><th rowspan="3">Input</th><th colspan="8">Aquatic animal production system</th></tr><tr><th colspan="2">Salmonid</th><th colspan="2">Cyprinid</th><th colspan="2">Molluscs</th><th colspan="2">Crustacean</th></tr><tr><th>Marine netpen (Atlantic salmon)</th><th>Freshwater pond (rainbow trout)</th><th>Subsistence-tropical (small scale)</th><th>Commercial (large scale)</th><th>Marine rope culture (mussel)</th><th>Bottom culture (bottom)</th><th>Land-based recirculation (shrimp)</th><th>Pond (shrimp)</th></tr></thead><tbody><tr><td>Feed</td><td>VH</td><td>H</td><td>L</td><td>M</td><td>Z</td><td>Z</td><td>L</td><td>M</td></tr><tr><td>Disease control (vaccination)</td><td>H</td><td>H</td><td>L</td><td>M</td><td>VL</td><td>VL</td><td>L</td><td>L</td></tr><tr><td>Biosecurity</td><td>H</td><td>H</td><td>L</td><td>M</td><td>VL</td><td>VL</td><td>H</td><td>M</td></tr><tr><td>Stocking density</td><td>H</td><td>H</td><td>L</td><td>M</td><td>L</td><td>L</td><td>VH</td><td>M</td></tr><tr><td>Energy</td><td>M</td><td>M</td><td>L</td><td>L</td><td>VL</td><td>VL</td><td>VH</td><td>M</td></tr><tr><td>Labour</td><td>L</td><td>M</td><td>H</td><td>L</td><td>L</td><td>L</td><td>M</td><td>M</td></tr><tr><td>Capital</td><td>M</td><td>M</td><td>L</td><td>L</td><td>L</td><td>L</td><td>H</td><td>M</td></tr><tr><td><strong>Overall intensity of input</strong></td><td><strong>H</strong></td><td><strong>H</strong></td><td><strong>L</strong></td><td><strong>ML</strong></td><td><strong>VL</strong></td><td><strong>VL</strong></td><td><strong>H</strong></td><td><strong>M</strong></td></tr></tbody></table>

H: high

M: medium

VH: very high

Z: zero (no inputs)

L: low

ML: medium low

VL: very low
## Approach to data collection

The GBADs approach aims to make use of existing production data through systematic literature reviews. Data gaps are addressed through expert elicitation. Production data will be most readily available for commercial salmonid production systems (salmonid and shrimp) and largely lacking for small-scale subsistence aquaculture (notably tropical freshwater cyprinid farming). Farmers' data may be considered commercially important or otherwise sensitive (e.g. mortality rates), which may present challenges around confidentiality and publication.

## Calculation of the Animal Health Loss Envelope

The GBADs programme is described in other articles in this issue. Fundamental to the GBADs approach is the description of populations under study, their value, the resources they consume and the products generated. Modelling the efficiency of the relationship between input and output for both current conditions and an 'ideal health' scenario (absence of disease) generates an 'envelope' of total disease burden that contains the sum of lost production due to disease and total additional resources used to mitigate disease and achieve current production in the presence of disease (e.g. expenditure on treatments, vaccinations) [11].

Gilbert et al. [12] calculated the AHLE at the national level for a representative broiler chicken sector. Under 'ideal'

conditions, veterinary costs, post-harvest rejection and mortality rates are set to zero. The food conversion ratio (FCR) and length of the production cycle are adjusted to a level that would be expected in the absence of disease (resulting in lower feed costs for the same production). For example, in the analysis of poultry production, FCR decreased from 1.6 to 1.41 for large broilers [12]. The input of purchased one-day-old chicks is reduced under ideal, compared with current, production, to keep output (chicken meat) and final stocking density unchanged between current and ideal conditions. The large majority (68%) of the AHLE is attributed to reduced feed costs.

The main sources for key production parameters (industry, government, published data and expert opinion) required for the AHLE calculation are summarised by the production system in Table II. Not all parameters are relevant for all systems; for example, molluscan systems have no feed costs. In some countries, industry is required to report mortality to the competent government authority, and these data may be available from official sources. Similarly, costs of water abstraction (freshwater) and seabed leasing are generally in the public domain. It is clear from Table II that expert opinion is required for most of the production parameters for subsistence cyprinid and small-scale shrimp production. If available, farm data from commercial aquaculture sectors can be used to quantify farm variation in production parameters, e.g. FCR and production cycle length. These analyses can inform estimates of production parameters achievable under ideal conditions.

<caption>**Table II**</caption>

Availability for production parameters by aquaculture production system – current production

<table><thead><tr><th rowspan="3"></th><th colspan="6">Aquatic animal production system</th></tr><tr><th>Salmonid</th><th colspan="2">Cyprinid</th><th colspan="3">Molluscs</th></tr><tr><th>Atlantic salmon/ rainbow trout</th><th>Subsistence – tropical (small scale)</th><th>Commercial (large scale)</th><th>Mussel/oyster</th><th>Recirculation (shrimp)</th><th>Pond (shrimp)</th></tr></thead><tbody><tr><th colspan="7">Production costs</th></tr><tr><td>Labour costs</td><td>ID and PD</td><td>EE</td><td>ID and PD</td><td>ID</td><td>ID</td><td>EE</td></tr><tr><td>Infrastructure</td><td>ID</td><td>EE</td><td>ID</td><td>ID</td><td>ID</td><td>EE</td></tr><tr><td>Water*</td><td>OS</td><td>NR</td><td>OS</td><td>OS</td><td>OS</td><td>OS</td></tr><tr><td>Veterinary costs</td><td>ID</td><td>EE</td><td>ID</td><td>NR</td><td>ID</td><td>EE</td></tr><tr><td>Energy costs</td><td>ID</td><td>EE</td><td>ID</td><td>ID</td><td>ID</td><td>EE</td></tr><tr><th colspan="7">Production parameters</th></tr><tr><td>FCR**</td><td>ID and PD</td><td>EE</td><td>ID and PD</td><td>NR</td><td>ID and PD</td><td>EE</td></tr><tr><td>Mortality rate (by stage of production)</td><td>ID and OS<br>IS</td><td>EE</td><td>ID and OS</td><td>EE</td><td>ID</td><td>EE</td></tr><tr><td>Harvest rejection</td><td>OS</td><td>NR</td><td>OS</td><td>NR</td><td>OS</td><td>OS</td></tr><tr><td>Carcass downgrading</td><td>OS</td><td>NR</td><td>OS</td><td>NR</td><td>OS</td><td>OS</td></tr><tr><td>Harvest weight</td><td>ID and OS</td><td>EE</td><td>ID and OS</td><td>ID and OS</td><td>ID and OS</td><td>ID and OS</td></tr></tbody></table>

EE: expert opinion required

FCR: food conversion ratio

ID: industry data

NR: not relevant

OS: official statistics

PD: published data

* for example, abstraction/seabed lease costs

** feed costs based on FCR
## Applying the Animal Health Loss Envelope to hatchery production

Many aquaculture systems are based on a relatively small number of hatcheries producing juvenile animals supplied to a considerably larger number of ongrowing farms. The application of the AHLE to hatchery production is more complex and subject to greater uncertainty compared with ongrowing farms, as the population comprises both breeding stock and juveniles destined for sale. Outputs from the farm include live fish for ongrowing and culled breeding stock for consumption. FCR and survival rates of broodstock and juveniles are required, as is the impact of disease on reproduction. Populations simulation modelling will be required to apply GBADs methods to breeding populations.

## Applying the Animal Health Loss Envelope to small-scale tropical finfish production

A range of production systems are used in small-scale freshwater pond finfish production systems in Asia. Polyculture is widely practised based primarily on indigenous and exotic species of fish. For example, in Bangladesh, the major indigenous cultured species are catla (Catla catla), rohu (Labeo rohita), mrigal (Cirrhinus mrigala) and kalbaush (Labeo calbasu), which may be co-cultured with exotic species: silver carp (Hypophthalmichthys molitrix), grass carp (Ctenopharyngodon idella), common carp (Cyprinus carpio), pangas (Pangasius sutchi), Thai silver barb (Barbodes gonionotus), tilapia (Oreochromis spp.) and hybrid magur (native Clarias batrachus x African catfish Clarias garipinus) [13]. In some systems, shrimp may also be introduced. Integration of fish with duck or chicken farming is also common. The AHLE would need to be separately modelled for each farmed species and then combined at farm level. It is possible that a significant element of the AHLE in small-scale backyard systems is attributable to suboptimal nutrition.

## Applying the Animal Health Loss Envelope to mollusc production

In ongrowing aquaculture systems, reduced feed costs are highly likely to account for a large element of the AHLE due to improved FCR and reduced mortality. However, molluscan production has no feed input. Under ideal conditions (i.e. optimal concentrations of microalgae and other food sources), molluscs may grow faster, but no studies exist to inform expert opinion on the time to harvest under current and ideal conditions. Optimal growth can be estimated based on growth rate data: the fastest observed growth could be used as an estimate of growth rate under ideal conditions. The AHLE would comprise a) increased production from reduced time to harvest and b) reduced cost of purchased animals from reduced mortality (all other variable costs would remain constant). While it is useful to know what proportion of the AHLE can be attributed to suboptimal nutrition, as

the system has zero feed inputs it is not amenable to intervention. The costs of mollusc production in many countries depend on water quality. Production in water that suffers little impact from anthropogenic activities (agricultural runoff, sewage discharges), e.g. class A waters under European Union classification, can be marketed directly. By contrast, production in which microbiological quality is poor (as measured by coliform counts) incurs additional costs from legally mandated interventions, notably depuration, before sale. If it is assumed that the burden of disease includes costs associated with product safety/market readiness, then under ideal conditions costs of depuration should be omitted.

## Applying the Animal Health Loss Envelope to recirculation aquaculture systems

The AHLE may provide new insight into the differences between recirculation aquaculture systems (RAS) and traditional aquaculture systems. Shrimp are produced in a range of systems, including small-scale and extensive pond production, and increasingly in RAS. RAS are epidemiologically isolated and therefore, compared with open water systems, inherently more biosecure. The environmental conditions (water quality) can be tightly controlled. While RAS are not disease-free, they generally operate with lower levels of mortality and morbidity compared with production of the same species in pond systems. In addition, the high level of biosecurity in RAS results in low levels of disease control costs. Thus, compared with pond systems, the AHLE will be smaller. The biosecurity costs derive from the high capital start-up and energy costs that are inherent to the system. Removing these costs under ideal conditions effectively changes the system and thus invalidates calculation of the AHLE.

## Case study: Animal Health Loss Envelope calculations for rainbow trout production in England and Wales

A key component of the salmonid aquaculture sector in England and Wales is the production of rainbow trout for human consumption by farms that purchase juvenile fish and grow them to harvest weight. An existing dataset, collected through expert elicitation and systematic literature reviews, was used to model the relationship between inputs and outputs of a site producing 350 metric tonnes of rainbow trout for human consumption per annum and to generate an AHLE estimate. Data were collected using the typical farm approach [14] (summarised in Table III). The total number of fish harvested was estimated using the known number of fish stocked and mortality estimates. Revenue was calculated as the product of number of fish harvested, the mean average individual fish harvest weight, and the farmgate price per kilogram. Feed cost was based on the FCR, feed cost per kilogram and total biomass produced (fish harvested and mortalities). Under 'ideal conditions', the factors of mortality, veterinary costs and annual
Table III

Rainbow trout typical farm model production parameters, prices and costs

Costs derived from the typical farm model

<table><thead><tr><th colspan="2">Production parameter</th></tr></thead><tbody><tr><td>Fingerling weight at stocking (g)</td><td>5</td></tr><tr><td>Fish stocked per annum</td><td>1.1 million</td></tr><tr><td>Fingerling mortality (%)</td><td>20</td></tr><tr><td>Ongrowing fish mortality (%)</td><td>10</td></tr><tr><td>Fingerling average weight at death (g)</td><td>37</td></tr><tr><td>Ongrowing fish average weight at death (g)</td><td>217</td></tr><tr><td>Average harvest weight (g)</td><td>450</td></tr><tr><td>Food conversion ratio</td><td>1.1</td></tr></tbody><thead><tr><th colspan="2">Price data (£)</th></tr></thead><tbody><tr><td>Cost of feed per kg</td><td>1.16</td></tr><tr><td>Farm gate price per kg</td><td>2.45</td></tr><tr><td>Purchase of fish (100)</td><td>10.45</td></tr></tbody><thead><tr><th colspan="2">Annual operating costs (£) (% total)</th></tr></thead><tbody><tr><td>Feed</td><td>489,389 (60)</td></tr><tr><td>Fish purchase</td><td>115,000 (14)</td></tr><tr><td>Veterinarian</td><td>9,000 (1)</td></tr><tr><td>Electricity</td><td>13,500 (2)</td></tr><tr><td>Oxygen and ice</td><td>24,000 (3)</td></tr><tr><td>Mortality removal</td><td>2,000 (&gt;1)</td></tr><tr><td>Other variable</td><td>3,000 (&gt;1)</td></tr><tr><td>Total fixed costs</td><td>89,000 (11)</td></tr><tr><td>Labour costs</td><td>65,000 (8)</td></tr></tbody></table>

costs associated with mortality removal were set to zero, and the number of fish stocked was reduced to achieve the same production under ideal and current conditions (it was assumed that stocking density at the point of harvest under current conditions was optimal). Other costs were unchanged between ideal and current conditions. The British Trout Association estimates that FCR for farmed rainbow trout in England and Wales ranges between 0.8 and 1.1 [15]. The FCR was reduced from 1.1 to 0.8 under ideal conditions (harvest size was unchanged). The AHLE was estimated to be £ 203,849 (compared with a revenue of £ 873,180) (Table IV), a 25% reduction in expenditure under ideal compared with current production. The majority (79%) of the AHLE was attributed to reduced feed costs, which decreased by 32%. The other key saving was reduced stocking costs as fewer fingerlings were purchased (as mortality was zero under ideal conditions). The analysis was at farm level and prices were assumed to remain constant. Scaling the analysis to national level should ideally involve the modelling of potential changes to farmgate price.

Discussion

Government decision-making regarding aquatic animal health and subsequent resource allocation often focus on diseases that have garnered political attention through

Table IV

Typical rainbow trout farm Animal Health Loss Envelope based on expenditure and output under current conditions with disease and ideal conditions without disease

<table><thead><tr><th></th><th>Current</th><th>Ideal</th><th>Net</th></tr></thead><tbody><tr><td>Ordinary input cost</td><td>£ 800,889</td><td>£ 606,039</td><td>£ 194,849</td></tr><tr><td>Disease control input cost</td><td>£ 9,000</td><td>£ 0</td><td>£ 9,000</td></tr><tr><td>Total output value</td><td>£ 873,180</td><td>£ 873,180</td><td>£ 0</td></tr><tr><td>Biomass valuation</td><td>£ 0</td><td>£ 0</td><td>£ 0</td></tr><tr><td></td><td>AHLE</td><td></td><td>£ 203,849</td></tr></tbody></table>

AHLE: Animal Health Loss Envelope

listing by the World Organisation for Animal Health (WOAH) [6]. WOAH-listed diseases have global significance and are generally highly infectious epidemic diseases that can spread through trade in animals and their products. As a consequence, the control of endemic diseases is often neglected. Information on the true cost of endemic disease can help redress this imbalance. GBADs methods offer a sound basis for both data collection and analysis to generate information on the burden of disease in aquaculture systems. This article has demonstrated that GBADs methods can be applied successfully to aquaculture. Specifically, the rainbow trout case study illustrates an AHLE calculation at farm level, which can be scaled for a sectoral analysis. A more accurate AHLE estimate requires better data on the occurrence of mortality over the production cycle and on variation in FCR within the industry. Nevertheless, the calculation presented here indicates the maximum possible benefit achievable through improved aquatic animal health intervention and is in line with a similar analysis of Norwegian farmed Atlantic salmon and rainbow trout at the national level, which indicated cost reduction of 31–38% under ideal compared to current production [16]. While achieving zero mortality and no expenditure on disease control is not a realistic goal, establishing the AHLE as an objectively defined standard representing the maximum benefit that can be achieved by eliminating disease burden overcomes many of the problems inherent in comparing different production systems [12]. It is an important first step in attributing burden to different causes.

All modelling involves simplification of complex biological systems. For example, it is not possible to model the relationship between mortality and stocking density in the calculation of the AHLE. Furthermore, for hatcheries and polyculture, the calculations are more complex. Further work is required to fully explore the application of the methods to zero feed molluscan production.
In many systems, notably small-scale tropical finfish pro-
duction, a lack of published data will be a key constraint.
Estimates of disease burden can be achieved across pro-
duction systems and at national level only if efficient, con-
sistent data collection and integration techniques are
developed and adopted by aquaculture producers. In
Atlantic salmon production, an approach to data collection
based on the cause of mortality, and on a logical hierarchy,
has been proposed [17] and could be applied to other sys-
tems. Government can support better data collection by
requiring as a condition of farm authorisation that mortality
(and potentially other parameters) be recorded, with infor-
mation that allows for attribution to cause. Importantly, farm-
ers need to benefit from data analyses to incentivise data
collection and sharing. Beyond attribution, value chain mod-
elling is needed to determine societal impacts of disease
burden. Rojas et al. [9] noted that the link between aquatic
production and post-production systems (e.g. value creation
in different product distribution models) is unclear. Thus, the
impacts of aquatic diseases on supply chain stakeholders
(e.g. processors, wholesalers) are difficult to address. The
gaps must be addressed to determine the societal, eco-
nomic, human nutrition and health, and gender impacts of
aquatic diseases and investments in disease control. Work
by Countryman and Shakil, overseen by Marsh and Pendell,
as part of the GBADs Ethiopian case study (papers currently
in review), has elaborated how the AHLE can serve as an in-
put to scenarios in wider economy models, generating esti-
mates of changes in gross domestic product and producer
and consumer surplus due to the burden of animal diseases.

Conclusions

This review demonstrates how GBADs methods, and notably
the AHLE, can be applied to aquaculture production systems.
Data availability is a key limitation in the calculation of the
AHLE. Ideally, production under ideal conditions would be
informed by experiment results, but in reality this calculation
is based on models, meta-analysis of peer-reviewed data or
expert opinion. Government has an important role to play in
facilitating data collection and analysis that support decision-
making by both governments and industry. The GBADs pro-
gramme is an important first step to generate evidence on
the cost of disease at the production-system and national
level to support decisions concerning investment in aquatic
animal health. Additional assessments are required to sup-
port government decision-making. Analyses of the costs and
benefits of animal health interventions, such as vaccination,
will allow prioritisation of mitigation measures. Determining
the environmental impact, both negative and positive, and
how the societal benefits of aquaculture are distributed will
support the development of national aquaculture strategies.

Acknowledgements

This paper has benefited from collaborations and conversa-
tions with many colleagues over recent years. The authors
acknowledge their contribution.

Application de la méthode « Impact mondial des maladies animales » aux systèmes de production aquacole

E.J. Peeler, E. Brun, B. Misund, W. Gilbert, B. Huntington, M. Reantaso, C. Walde & A. Kennerley

Résumé

Les principaux objectifs du programme « Impact mondial des maladies animales » (GBADs) visent à fournir une méthode systématique pour déterminer l'impact des maladies animales et sont pertinents aussi bien pour les systèmes de production d'animaux terrestres que pour les systèmes aquacoles. Néanmoins, à ce jour, les méthodes du GBADs ont surtout été appliquées aux systèmes de production d'animaux terrestres. Les difficultés d'application des méthodes du GBADs, en particulier le calcul de l'enveloppe des pertes sanitaires animales varient considérablement d'un système de production à l'autre. Les auteurs décrivent la méthode appliquée pour calculer l'enveloppe des pertes sanitaires animales dans les élevages de truites arc-en-ciel en Angleterre et au pays de Galles, méthode dont ils reconnaissent que l'application à d'autres systèmes (par exemple la production en écloserie, la polyculture et la production de mollusques sans intrants de fourrage) est plus complexe. Par exemple, dans la production de poissons tropicaux à petite échelle, l'impact d'une nutrition sous-optimale sur la production devrait être pris en compte. Les systèmes de recirculation fermée en aquaculture garantissent intrinsèquement des niveaux élevés de biosécurité et de contrôle sanitaire qui se traduisent par un niveau faible de maladies. La suppression des coûts d'investissement et
de fonctionnement associés à la biosécurité modifie fondamentalement le système et invalide le calcul de l'enveloppe des pertes sanitaires animales. Compte tenu de l'absence de données disponibles concernant un grand nombre de systèmes, notamment les petits élevages de poissons tropicaux, il faudra recourir aux avis d'experts pour étayer l'ap- plication des méthodes du GBADs. Si l'article aborde essentiellement le calcul de l'enveloppe des pertes sanitaires animales, les auteurs signalent l'importance de rechercher les causes et de modéliser les chaînes de valeur afin de générer des données représentatives de l'impact sociétal au sens large des maladies affectant les animaux aqua- tiques (ainsi que des interventions envisageables), outils indispensables pour étayer les décisions gouvernementales concernant les ressources à allouer.

## Mots-clés

Aquaculture - Crevette - Économie - Enveloppe des pertes sanitaires animales - GBADs - Impact des maladies - Impact mondial des maladies animales - Santé animale - Truite.

# Aplicación de la metodología del Impacto Global de las Enfermedades Animales a la producción de animales acuáticos

E.J. Peeler, E. Brun, B. Misund, W. Gilbert, B. Huntington, M. Reantaso, C. Walde & A. Kennerley

## Resumen

El objetivo principal del programa sobre el Impacto Global de las Enfermedades Animales (GBADs), a saber, pro- porcionar un enfoque sistemático para determinar el impacto de dichas enfermedades, es tan pertinente para los sistemas de producción de animales acuáticos como terrestres. Sin embargo, hasta la fecha, los métodos del GBADs se han aplicado principalmente a los sistemas de producción de animales terrestres. Las dificultades que plantea la aplicación de los métodos del GBADs, en particular la cartera de pérdidas en sanidad animal, varían considerable- mente según el sistema de producción. Los autores demuestran cómo puede calcularse la cartera de pérdidas en sanidad animal para la producción de trucha arco iris en Inglaterra y Gales y reconocen que su aplicación en otros sistemas (por ejemplo, la producción en viveros, el policultivo y la producción de moluscos sin insumos alimentarios) es más compleja. Por ejemplo, en la producción de peces tropicales a pequeña escala habría que abordar el impacto de una nutrición subóptima en la producción. Los sistemas de recirculación en acuicultura conllevan altos niveles de bioseguridad y control de enfermedades y, por lo tanto, bajos niveles de enfermedad. Si se eliminan los costos de capital y de explotación asociados a la bioseguridad, el sistema cambia radicalmente e invalida el cálculo de la cartera de pérdidas en sanidad animal. La falta de datos de muchos sistemas, especialmente de la cría de peces tropicales a pequeña escala, implica que se necesitará la opinión de expertos para apoyar la aplicación de los métodos del GBADs. Aunque el presente artículo se centra en el cálculo de la cartera de pérdidas en sanidad animal, cabe señalar que la determinación de las causas y la modelización de la cadena de valor son necesarias para generar datos sobre el impacto social más amplio de las enfermedades de los animales acuáticos (y las posibles intervenciones), que los gobiernos necesitan para respaldar la toma de decisiones sobre la asignación de recursos.

## Palabras clave

Acuicultura - Camarón - Cartera de pérdidas en sanidad animal - Economía - GBADs - Impacto de las enfermedades - Impacto Global de las Enfermedades Animales - Sanidad animal - Trucha.

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