Andy Shinn

Parasites of fish and shrimp

The eyelash mite (Demodex

folliculorum), or the

demodicid, lives harmlessly

in the eyelash follicles of

around 98% of us.

Examined 21,787 hosts

137,230 metazoan parasite species

Man561

6.3 parasite species per host

Sheep388

Dog377

Cow356

Duck342

Horse264

Fox217

Common carp 300Roach 222Bream 190Tuna 174

Nile tilapia 60Pangasius 16

Penaeus monodon 2

There are a lot of parasites out

there!

So how many parasites are there? 32,000 species of fish3,000 caridean species

Pre-harvest mortalities result from the complex interplay of broad range of factors, including:

Stock source / genotype Developmental defectsPredation /cannibalism Impaired nutritionPhysical damage Sub-optimal /hostile Disease environmental conditions

Economic losses, in addition to mortalities, can result from:

Impacts on growth / food conversionPost-harvest downgrading of productsFish escapesManagement decisions that impact on profitability

e.g. delayed decisions to treat, grade, harvestCosts of husbandry and management practices

e.g. fallowing, grading, vaccination, treatment etc

…. and parasites of course!

The frequent association of disease with other pre-disposing,such as poor water quality and the broad range of events thatmight stress farm populations, also means that untangling theimpacts of disease from those linked to other causes becomesvery difficult or near impossible.

So in many cases the economic impact of parasitic diseases can only be estimated. Their role in subsequent infections is equally difficult to estimate, i.e. through the action of parasites, they facilitate subsequent viral, bacterial and fungal infections.

Anisakid nematodes

90

80

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20

10

0

Glo

bal

aq

uac

ult

ure

pro

du

ctio

n(m

illio

ns

of

ton

s)Blue: Global production

Red: Asian production

Asian and global aquaculture has been consistently

increasing at 6.4% p.a. over the last 5 years and at 7.2%

since 2010.

90.4 M t

82.1 M t

92

90

88

86

84

82

80

Asi

a co

ntr

ibu

tio

n t

o g

lob

alaq

uac

ult

ure

pro

du

ctio

n (

%)

Asia, for the past 20+ years, accounts for over 90% of

global aquaculture production

90.78% in 2012

1980 1990 2000 2010Year

Blue: Global aquaculture production

Red: Asian aquaculture production

Data from FAO FishStatJ

Here we see the impact of certain

disease events on the Asian shrimp industry, as an example of one

industry, with estimates of the resultant losses.

Global (blue line) and Asia’s (red line) year-on-year growth presented as a percentage

Costs of shrimp disease

1. US$ 0.3 B: YHV and WSSV in Indonesia;2. US$ 30-40 M p.a.: YHV in Thailand;3. US$ 0.5 B: WSSV in China;4. US$ 100 M: WSSV, YHV and MBV in

Vietnam;5. Losses in Thailand due to WSSV and

THV rise from US$ 240 M to 650 M p.a.; 6. US$ 160 M p.a.: WSSV in Sri Lanka;7. US$ 25 M: WSSV in Malaysia;8. US$ 80 M: WSSV in India;9. US$ 0.4 B: All shrimp diseases;10. US$ 3 B : “EMS” in Thailand. Exports

down 32% year-on-year. The value has declined by 17% to US$ 1.16 B.

So what about the impacts of parasitic diseases?

These can be divided into two categories:

Unpredictable / sporadic

Predictable / regular

For both, there may be costs in treating and managing infections once established, but for predictable infections there will also be costs associated with prophylactic treatment / management.

Perennial costs, e.g. associated with the management and control of sea lice (Lepeophtheirus and Caligus), can be largely predicted throughout a production cycle as they pose a continuous threat to captive stocks of fish.

The life-cycle, timings and dynamics of the parasiteare well understood.

Parasite numbers are continuously monitored to ensure they do not cross threshold levels.

Sea lice can be controlled through the employment of an integrated pest management strategy involving the use of a broad range of management tools in addition to direct treatment interventions.

Photo © J. Bron

Sea lice control in Norway in 1996 was about US$ 33.4 M, by 2009 this was US$ 206 M. Over the same time period, Norwegian salmon production increased by 248% (298 TT to 738 TT) and yet, the price of salmon increased only 20% (US$ 3.08-3.71 kg-1).

As sea lice impose this consistent threat, infections can be predicted and factored into farm business plans and farm-level treatment strategies.

Over the same time, there have been sig. improvements in salmon welfare, and the number of sea lice-related mortalities and the number of fish downgraded as a consequence of sea lice damage has fallen dramatically. To achieve this, the basic costs of sea lice control have increased from 3·64% in 1996 of total production costs to 7·53% in 2008.

For many new or less-established industries (esp. those restricted to a smallnumber of production sites), the parasite threats may be largely unknown andemerging, and new infections can have a devastating impact. The impact andseverity of Paramoeba perurans (AGD) infections on the early Tasmanianproduction of rainbow trout serves as an appropriate example.

Image © C. Matthews

Of course, established industries can also be hit, e.g. an outbreak of AGD inScotland in 2011 resulted in the loss of 13,600 tons of Atlantic salmon worth anestimated US$ 81 M.

Image © C. Matthews

Kingfish, Seriola lalandi, SE AustraliaPhoto: I. Ernst / C. Chambers

Parasite Host Country Year US$ (M)Kudoa yasunagai Japanese amberjack Japan 2011 1.6Paramoeba perurans Atlantic salmon Tasmania 2001 5-10Uronema nigricans S. bluefin tuna Australia 2003 2.13

Benedenia seriolae Amberjacks Japan/Aus 2001-14 214Benedenia seriolae Amberjacks Australia 2010 3.7*Caligus chiastos & S. bluefin tuna Australia 2008 1.4Cardicola forsteriHeteraxine heterocerca Japanese amberjack Japan 1963 1Neobenedenia melleni Amberjacks Japan 2014 >200Neobenedenia melleni Cobia Taiwan 2001 1.8Neobenedenia melleni Cobia Taiwan 2003 0.9

If we consider some major parasite events on fishin Asia

And some on crustaceans ….

Parasite Host Country Year US$ (M)

Haplosporidian sp. Whiteleg shrimp Indonesia since 2007 >5

Hematodinium sp. Indo-Pac. sw. crab Guangdong 2005-08 11.6-12Scylla serrata Prov., China p.a.

National, China 2005-08 352 tot

Hematodinium sp. Swimming crab Shandong, China 2004-12 6.7-13 p.a.P. trituberculatus National, China 2004-12 31.6 p.a.

National, China 2004-12 285 tot

‘Cotton shrimp disease’ in cultured penaeid shrimp

uninfected

infected

microsporidian pathogen

500 nm

TEM: spore of Spraguea sp. from anglerfish Lophius spp.

Lamellar

polaroplast

Anchoring

disk

Polar

filament

Tangprasittipap et al. (2013)

Enterocytozoon hepatopenaei and others!

Enterocytozoon hepatopenaei (EHP)First described from Thailand in 2009 in farmed, giant tiger shrimp P.monodon and then later P. vannamei;Confined to the hepatopancreasFound in slow growing shrimp but statistically so?Does not cause mortality;Direct transmission from shrimp to shrimp by the oral route;

Can be tested for using specific primers in our labNon-destructive testing

Speak to Pikul

There are a number of concerns associated with the expansion of

global aquaculture:

.

Rio de Janeiro, Brazil

Global population is currently 7.17 B and expected to be 9.55 B (i.e.

33% increase) by 2050.

Expansion of global aquaculture within the coastal zone.

Human migration to the coast (53% of the US population reside in

17% of coastal land area). Population living in the coastal zone is

expected to increase by 24.4% by 2025.

Increased human activity and increased nutrient inputs in an era of

changing climatic conditions is likely to have further impacts on

water quality, aquaculture production and the prevalence and

severity of disease events.

A significant proportion of stock losses occur within the hatchery / nursery phasesof production and in many industries these are factored into and “accepted” aspart of normal operational practices.

A significant proportion of stock losses occur within the hatchery / nursery phasesof production and in many industries these are factored into and “accepted” aspart of normal operational practices.

Such fatalistic acceptance of their inevitability means that they are frequently underreported, hiding the severity and impact of certain parasites.

Zoothamnium duplicatuminfestation of cultured

horseshoe crabs(Limulus polyphemus)

Shinn et al. (2015)

Mortality of 40,0002nd/3rd instar larvae

(i.e. 96%)

10 20 30 40 50

25

20

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10

5

0

Mill

ion

s

Weeks

Eggs Swim-up21 d postmonosex

1” postnursery

Survival metrics across one cluster of Oreochromis niloticus sites (n = 4)

Survival metrics across one cluster of Oreochromis niloticus sites (n = 4)

Eggs

14.85 M month-1

Hatch rate 77.5%

11.50 M month-1

s.e. = starting egg number

Swim-up

77.8% survival(60.85% of s.e.)

9.0 M month-1

21 d postmonosex

78.9% survival(48.0% of s.e.)7.1 M month-1

1” postnursery

83.3% survival(40.0% of s.e.)

5.9 M month-1

Economics of juvenile loss

Eggs toswim-up

Monosexto nursery

Swim-up tomonosex

2.47 M 1.91 M 1.19 M

0.1 THB 0.3 THB0.2 THB

Farm data suggests that approx. 20% of stockare lost to parasites

US$ 3075 US$ 3560 US$ 2950

So this collection of site are losing

US$ 9,585 month-1

Causes of juvenile loss

20%parasites

Viral, bacterial,

other

Parasitesfacilitating 2ndry

infections ??

In 2012, there was a total of 43.59 M tons of fish produced of which 4.506 M tons was tilapia

Photo © R. Meyer / FVG

Using our earlier estimates, we can calculate juveniles losses as:

Lower (US$ M) Upper (US$ M)Nursery 4.48 6.17Monosex 5.41 7.43Swim-up 4.75 6.53

Total loss 14.64 20.12 (global tilapiaindustry only)

If we assume an av. sale weight of between 0.4-0.5 kg fish-1

8.2 to 11.3 billion tilapia being sold each year

If adjust for a further est. loss of 10% loss between nursery and harvest then we can estimate 9.0 -12.4 billion post-nursery fish

If apply this across global fish production, then the cost of parasites on juvenile production is somewhere between US$ 141.63 - 194.64 M

If we consider global production:

tons (M) US$ (M)FW prod 37.76 62,270Mar+Brackish prod 5.83 25,231Total 43.59 87,501

Parasite losses can be estimated at US$ 1070 – 4570 M

… and losses in growout (US$ M), then we can consider:

1.0% 2.5% 5% Juvenile141.63-194.64 *

Total growout 875 2188 4375Total (lower) 1017 2329 4517

(upper) 1070 2382 4570

Again applying 20% loss due to parasites

So we can see parasites can be costly but how do we begin to address these parasite problems?

Disease surveillance

A system of periodic monitoring of fish health should be implemented.

This monitoring has three levels of observations:

Level 3 – Samples sent to Level 2 could, additionally, be analyzed by advanced diagnostic techniques molecular biology techniques, PCR, qPCR, etc, where appropriate and guided by the findings from Level 2. This level of health assessment should be undertaken in specialised laboratories.

Level 1 - Macroscopic examination of the fish and wet mount analysis of fresh tissues under a light microscope / stereoscope. This level of observation can be done at the farm on a weekly basis by trained technicians. If the observations at level 1 reveal some anomalies, then specimens should pass to Level 2.

Level 2- Histological analysis. Samples of fish showing anomalies showed be fixed in 10% neutral buffered formalin and sent for histological analysis. This technique is carried out in specialized laboratories.

Before embarking on a course of treatment, it is important to have a proper identification ofthe causative disease agent and a clear understanding of its life-cycle.

This process involves a thorough examination of a sample of infected hosts as well as consideration of data concerning the fish’s environment, in order to collect all the information necessary to make aclear diagnosis.

An inaccurate diagnosis can either lead to the true problem going undiagnosed and becoming worse or can lead to an inappropriate course of treatment being used.

“Know thy enemy and know yourself; in a hundred battles, you will never be defeated"(Sun Tzu, 496 BCE)

Images from internet

The management and control of parasitic infections in aquaculture are a constant challenge, highly complicated by:

the current limited availability of efficacious licensed products

the development of resistance (to certain anti-parasitic drugs)

requirement to consider environmental, water quality and host parameters

the constraints of economics

the requirement for aquaculture sustainability and environmental protection

Treatment considerations

Delivering the right dose

“The right dose of the right drug to the right patient at the right time”

Sidney Taurel, 2005 (former CEO of Eli Lilley)

Having made an appropriate identification and decided upon a treatment, itis imperative that the pathogen is exposed to the correct target dose.Overdosing, in addition to imposing unwarranted additional expense andincreasing potential environmental impacts, can lead to the loss of stock,particularly when using chemicals with narrow safety margins.

Images from internet

While parasite impact in aquaculture is considerable, efficacious options for intervention other than anti-parasitic drugs remain limited

Fallowing and liming

Single year class stocks Non-chemical interventions

Feed management/ organic loading

Removal of reservoirs of

disease

Proper biosecurity and disinfection

protocols

Which treatment strategy to use?“…. let your methods be regulated by the infinite variety of circumstances”

(Sun Tzu, 496 BCE)

Image from internet

Experience has shown that while there are some rules of thumb that can be applied to the

treatment of certain parasitic infections, it is vital that the particulars of each situation are carefully

considered before a course of treatment is recommended.

Such “particulars” might include a diagnostic evaluation of:the current health status of the population to be treated; the severity of the infection(s); the pathology induced;water quality;the size of the fish population; and,the environment to be treated.

Image from internet

All of these need to be considered how we treat, when we treat, and what we treat with

Use and control of medicines and chemicals.

Technicians should know and understand when, how and

where to use licensed chemicals and medicines.

Ideally these responsibilities should fall on the

veterinarian in charge of the Aquatic Health Plan.

FVG Asia wet lab in Chonburi

Challenge room

Nursery

Lab External tank area

FVGAL main site

FVGAL wet lab

Premises were acquired in November 2014Renovated throughout Dec 2014Facility includes a small labHatchery room currently housing 3 × 400 L tanksAn external area with 32 × 200 L tanksA challenge room that can accommodate 50 × 10 L tanks

Wet lab in mid-Dec

The first major trial is already running

Flexibility for bespoke design to meet individual experimental needs.

External temperature regulation using a double skinned insulated roof with recirculating sprinkler system.

Experienced staff / 24 hour cover.

Back-up generator and air blowers.

On site challenge work and disease testing using iiPCR for known pathogens.

Electronic instrumentation, DO meters, data loggers.

Microscope with image capture.

A range of trials can be conducted at the wet lab including:

Bacterium / viral challengeGrowth / feed trialsPalatabilityParasite culture and infectionTreatment chemotherapy trialsLC50 / toxicity trialsHistopathology

Parasitology

498

Freshwater study is in prep

Whiteleg shrimp on sale at a market in Chonburi

Thank you for your kind attention

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