Biosecurity is salmon production

PRESENTATION

BROCHURE

BIOSECURITY IN SALMON PRODUCTION

Sandra Bravo

Biosecurity in Salmon Production

This work reviews the key points in salmon farming, from the diseases that affect the species and risk factors that favour the introduction and spread of pathogens, to the legal aspects related to biosecurity. The overall aim is to arm professionals with the tools they need to implement prevention-based health management that focuses on salmon welfare.

BIOSECURITY IN SALMON PRODUCTION

Sandra Bravo

TARGET AUDIENCE:

✱✱ Production animal vets. Aquaculture ✱✱ Animal production technicians ✱✱ Veterinary students ESTIMATED FORMAT: 11 × 20 cm RETAIL PRICE NUMBER OF PAGES: 96 NUMBER OF IMAGES: 44–66 BINDING: hardcover, wire-O

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Author SANDRA BRAVO Associate lecturer at the Institute of Aquaculture, Austral University of Chile. Associate editor of the Latin American Journal of Aquatic Research.

KEY POINTS:

➜➜ Handy, user-friendly format. ➜➜ Includes the most pertinent and latest issues regarding salmon production. ➜➜ Focuses on biosecurity and animal welfare.

Biosecurity in Salmon Production

Presentation The World Organisation for Animal Health (OIE) defines biosecurity as a set of management and physical measures designed to mitigate the risk of introduction and spread of pathogenic agents in animal populations subject to intensive production.

Salmon farming is an intensive production activity and as such entails certain health risks. However, in the specific case of fish, the health risks are even greater given the difficulty of isolating and eradicating the pathogens found in an aquatic environment and the scarcity of therapeutic agents for use in aquaculture. Faced with this situation, biosecurity takes on special relevance because the level of risk depends on the fishes’ developmental stage and the production systems in place.

All salmon-producing countries reinforced their biosecurity measures following the arrival of the infectious salmon anaemia (ISA) virus. The first outbreak of ISA virus was recorded in Norway in 1984, prompting health authorities to implement regulations based on biosecurity measures to minimise the risk of the disease’s occurrence and spread.

The ISA virus can now be found across all salmon-producing Atlantic countries in the northern hemisphere and an outbreak in Chile was reported in 2007. To date, the ISA virus has been kept under control thanks to the strict biosecurity measures implemented by the health authorities in each country where the disease has emerged, and its presence is only recorded when the production or environmental conditions are unsuitable for the fish. However, despite the application of stringent biosecurity regulations and measures, infectious diseases still represent the foremost threat to farmed salmon, primarily in open production systems such as sea pens or cages.

This manual is intended for professionals working in salmon production and its main objective is to provide them with knowledge and guidelines on prophylaxis and preventive steps to minimise the risk of introducing and disseminating pathogens in bodies of water.

It includes topics related to the basic principles of epidemiology; infection and disinfection mechanisms for the main diseases that affect farmed fish; and the implementation of biosecurity measures in production farms, by providing tools that contribute to health management based on disease prevention and fish welfare.

The author Sandra Bravo Sandra graduated in fisheries management from the Pontifical Catholic University of Valparaíso (Chile) with an undergraduate dissertation in the area of fish pathology. She obtained a master’s degree in aquaculture and environmental management at the University of Genoa (Italy) and a PhD from the Norwegian School of Veterinary Science (NVH) with a thesis on the sea louse Caligus rogercresseyi, a parasite that has become the main threat to the Chilean salmon farming industry.

From 1982 to 1987, she was head of the technical department at the first salmon farming company to operate in Chile (Pesquera Mares Australes) where she was responsible for health management and fish production, as well as directing research and development activities. Between 1987 and 1994, Sandra was the general manager at the first private laboratory in Chile (SalmoLab S.A.) providing fish pathology services to the salmon sector.

She acted as a consultant on issues related to health management in salmon farming for Chilean and international companies from 1982 to 1997. At the same time, she lectured on fish pathology and salmon production in nearby universities. From 1998 to the present, she has been an associate lecturer at the Austral University of Chile’s Institute of Aquaculture where she teaches pathology of aquatic organisms and salmon production to undergraduate and postgraduate students.

Biosecurity in Salmon Production

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Between 1998 and 2018, Sandra participated in 14 research projects and wrote 5Â book chapters and 9Â case studies. She has also published 37 articles in high-impact journals and 81 papers in aquaculture journals. Besides giving seminars at Chilean and international conferences, she has participated as a member of scientific committees for Chilean and international meetings. Since 2015, she has worked as associate editor of the Latin American Journal of Aquatic Research (LAJAR) and assessor for a series of high-impart journals.

Table of contents 1. Basic principles of fish pathology in salmon production 2. Salmon production systems Freshwater production systems Seawater production systems Water quality and fish health

3. Diseases affecting farmed salmon Viral diseases Bacterial diseases Parasitic diseases Fungal diseases

4. Disinfection products and protocols for pathogen control Action and effectiveness of the disinfectants Disinfection protocols

5. Biosecurity measures in production farms General biosecurity measures Biosecurity in hatcheries Biosecurity among breeding stock Biosecurity in fattening centres Biosecurity in stock and slaughter centres

6. Biosecurity in transport Transport of live fish Transport of harvested fish

7. References

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BIOSECURITY IN SALMON PRODUCTION

Sandra Bravo

BIOSECURITY IN SALMON PRODUCTION

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In 1980 in Japan Pacific salmon

In 1986 in Australia Rainbow trout

Herpesvirus Oncorhynchus masou virus disease (OMV)*

RNA

Freshwater Iridoviridae Epizootic hematopoietic necrosis*

DNA

In 1988 in Canada Pacific salmon RNA

Freshwater Seawater

In 1985 in Norway

In 2015 in Norway Atlantic salmon

Atlantic salmon

Seawater

Seawater RNA

In 1999 in Norway Atlantic salmon Coho salmon Rainbow trout Freshwater Seawater RNA

In 1938 in Denmark

In 1953 in the United States

Rainbow trout

Salmon and trout Freshwater RNA

RNA

Freshwater Seawater

In 1976 in Scotland

Rainbow trout Atlantic salmon Freshwater Seawater

In 1941 in the United States

Atlantic salmon Seawater

RNA

RNA

RNA/DNA

Retroviridae

in experimentally infected fish. It is not known how long the

Plasmacytoid leukaemia

the virus is 24 weeks, after which the first clinical signs appear

Totiviridae

route of infection is through the gills. The incubation period of

Paramyxoviridae/Poxviridae

blood, mucus, urine, faeces, and sexual fluids, and the main

Proliferative gill disease

The ISA virus is transmitted horizontally in the sea through

Piscine myocarditis

Mechanisms of infection

Reoviridae

brown trout (Salmo trutta) may act as asymptomatic carriers.

Heart and skeletal muscle inflammation

observed that rainbow trout (Oncorhynchus mykiss) and

Rhabdoviridae

salar) in seawater (Fig. 1) and it has been experimentally

Infectious hematopoietic necrosis*

al., 2008). The virus severely affects Atlantic salmon (Salmo

Rhabdoviridae

in the State of Maine (USA), and in 2007 in Chile (Godoy et

Viral haemorrhagic septicaemia*

the west coast of Scotland, in 2000 in the Faroe Islands and

Togaviridae

reported in 1996 in New Brunswick (Canada), in 1998 on

Family

myxoviridae. It was first described in Norway in 1984. It was

Disease

Disease caused by a virus belonging to the family Ortho-

Table 1. Main diseases of viral aetiology in salmonids.

Infectious salmon anaemia (ISA)

Causal agent

species worldwide (Table 1).

Birnaviridae

mainly affecting Atlantic salmon, the most commonly farmed

Infectious pancreatic necrosis

or cages at sea, a number of viral diseases have emerged,

Pancreatic disease*

In 1984 in Norway Atlantic salmon Rainbow trout Brown trout

Habitat

However, due to the intensive production of salmon in pens

Seawater

The first virus to be reported in salmonids was the haemorrhagic septicaemia virus (HSV) in 1938 in Europe.

RNA

gills.

Orthomyxoviridae

transmission occurs directly by contact, mainly through the

Infectious salmon anaemia*

effective drugs or vaccines to combat them. Horizontal

1st occurrence

against viruses affecting fish is essential, as there are no

Affected species

The implementation of biosecurity and preventive measures

Nucleic acid

VIRAL DISEASES

*Disease notifiable to the OIE

3 Diseases affecting farmed salmon

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BIOSECURITY IN SALMON PRODUCTION 3 Diseases affecting farmed salmon

virus can remain infectious in the natural environment. There is no evidence of vertical intraovarian transmission.

Mechanisms of infection The disease is transmitted horizontally. The virus is eliminated through faeces and mucus. Probable infection routes are the gills and intestinal tract. The virus survives in seawater for at least 21 days and some studies suggest that it may remain infective for approximately 63 days in sterile seawater at a temperature ≤10 °C, and survive for 14 days at 10 °C and 35 days at 4 °C in nonsterile seawater (Graham et al., 2007).

Inactivation methods The virus is rapidly inactivated in the presence of high Figure 1. Atlantic salmon infected with infectious anaemia virus. Image courtesy of Marcos Godoy.

concentrations of organic matter at 60 °C at a pH of 7.2, and at a pH below 4 or above 12 at 4 °C, which indicates that both silaging and alkaline hydrolysis are effective for

Inactivation methods Infectious salmon anaemia virus (ISAV) isolated in cell cultures can survive for weeks at low temperatures, but loses

inactivating the virus (Graham et al., 2007). Disinfection of eggs with iodophors prevents transmission of the virus (Graham et al. 2007).

its infectivity within 30 minutes at 56 °C (Falk et al., 1997).

It is sensitive to UV radiation and ozone. It is inactivated at a pH below 4 or above 12 for 24 hours and if exposed to a concentration of 100 mg/ml of chlorine for 15 minutes (Rimstad et al., 2011). Disinfection of embryonated eggs with iodophors eliminates the risk of vertical transmission.

Pancreatic disease (PD) Disease caused by an alpha virus belonging to the family Togaviridae, which is highly infectious and affects Atlantic salmon mainly in the first year of breeding in the sea (Fig. 2). The disease was first recorded in Scotland in 1976 and described in 1984 (Munro et al., 1984). To date, it has been reported in the United States and Europe, with Ireland, Norway and Scotland being the countries where it has had the most impact.

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Figure 2. Healthy Atlantic salmon (top) and Atlantic salmon with pancreatic disease (bottom). Image courtesy of Trygve Poppe.

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BIOSECURITY IN SALMON PRODUCTION 3 Diseases affecting farmed salmon

Infectious pancreatic necrosis (IPN) Disease caused by a birnavirus. It was first reported in 1941 in the United States. It was initially described as a highly contagious disease for rainbow trout and brook trout fry, in which mortality rates of up to 100 % were observed in fish between 1 and 4 months of age. In 1964, the first IPN outbreak was reported in Europe, in rainbow trout fry in France.

Another outbreak was then reported in rainbow trout in 1975 in Norway, and in 1985, the first case of the disease was diagnosed in Atlantic salmon fry in Norway (Krogsrud et al. 1989). The virus has now been reported in all countries where salmon is grown in both freshwater and seawater, and it is commonly diagnosed in Atlantic salmon in the first

Figure 3. Atlantic salmon infected with infectious pancreatic necrosis virus.

Image courtesy of Marcos Godoy.

months following their transfer to sea sites (Fig. 3) (Roberts and Pearson, 2005). The IPN virus has been harvested from at least 67 species of salmonids, nonsalmonids, crustaceans, and molluscs.

Viral haemorrhagic septicaemia (VHS) The aetiological agent is a virus from the Rhabdoviridae

Mechanisms of infection

family. The disease was first detected in 1938 in Denmark,

The virus is transmitted horizontally and vertically and elim-

where it was called Engtved disease. It has been detected in

inated through faeces and mucus. Fry are infected by

most continental European countries and the virus has also

transovarian transmission. Adult specimens that survive can

been isolated in Switzerland and Finland. The virus was first

act as reservoirs, acting as carriers for years, both in farmed

isolated in 1988 in the state of Washington (USA). Rainbow

and free environments, until the conditions are favourable for

trout is the most susceptible species (Fig. 4). Viral haemor-

the development of the disease. The IPN virus can survive for

rhagic septicaemia has also been reported in brown trout,

up to 17 days in untreated freshwater, 27 days in estuary water,

chinook salmon, coho salmon and Atlantic salmon. Fish

and 17 days in seawater at 15° C (Toranzo & Hetrick, 1982).

between 200 and 300 g are the most susceptible. Mortality can occur at temperatures between 3 and 12 °C. The dis-

Inactivation methods

ease is less severe above 15 °C.

Numerous studies have shown that the IPN virus is more

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resistant to disinfection treatments than other viral agents.

Mechanisms of infection

Disinfection of eggs with iodophors removes only viral parti-

Transmission is horizontal by contact with other fish or con-

cles on the surface of eggs and does not remove viral par-

taminated water. Infected fish excrete the virus in urine and

ticles inside the eggs.

sexual fluids (Wolf, 1988a). The virus persists in freshwater 7

BIOSECURITY IN SALMON PRODUCTION 3 Diseases affecting farmed salmon

from 28 to 35 days at 4 °C (Parry and Dixon, 1997) and has been found to be infective for 1 year at 4 °C in filtered freshwater (Hawley and Garver, 2008).

Inactivation methods The virus is susceptible to commonly used disinfectants.

Disinfection of embryonated eggs with iodophors eliminates the risk of vertical transmission.

Figure 5. Rainbow trout with infectious hematopoietic necrosis. Image courtesy of Jim Winton.

Mechanisms of infection It is transmitted horizontally and the main infection route is the gills. The virus is excreted in urine, sexual fluids and Figure 4. Rainbow trout infected with haemorrhagic septicaemia virus.

Image courtesy of Dieter Fichtner.

Infectious hematopoietic necrosis (IHN) Disease caused by a virus from the Rhabdoviridae family.

It was first reported in 1953 in sockeye salmon (Oncorhynchus nerka). In 1958, the first outbreak in chinook salmon was reported in the United States. It is an endemic disease in North America and Japan. It was first recorded in France and Italy in 1987. The IHN virus has not been detected in the southern hemisphere. It infects salmonids mainly in their fry stage. Rainbow trout is the most susceptible species (Fig. 5).

It also affects Atlantic salmon and the different varieties of Pacific salmon (Oncorhynchus nerka, O. tsachwystcha, O. keta, O. masou, O. rhodurus, O. kisutch). Outbreaks of

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mucus. The kidney, spleen, and other internal organs are the sites where the virus is most abundant during the course of infection (Bootlan and Leong, 1999). The virus survives in freshwater for at least one month at low temperatures, particularly in the presence of organic matter, and for several weeks at 15° C outside the host.

Inactivation methods The IHN virus is labile to heat, acidity and ether. It is easily inactivated in the presence of commonly used disinfectants and by drying (Wolf, 1988b). At 56° C, it is inactivated within 30 minutes. Disinfection of embryonated eggs with iodophors eliminates the risk of vertical transmission.

Heart and skeletal muscle inflammation

IHN can be acute and chronic. In acute outbreaks, cumula-

Disease caused by the Piscine reovirus (PRV), a double-

tive mortality may reach 90–95 % (Bootlan and Leong, 1999).

stranded, nonenveloped RNA virus. The first case was 9

BIOSECURITY IN SALMON PRODUCTION 3 Diseases affecting farmed salmon

reported in Atlantic salmon in 1999 in Norway (Palacios et al., 2010). It is an enzootic virus found in Chile, Ireland, Brit-

Proliferative gill disease (PGD)

ish Columbia (Canada), and the states of Washington and

This disease affecting the gills of Atlantic salmon has been

Alaska (USA). It has also been recorded in coho salmon,

associated with two viruses: the Atlantic salmon paramyxo-

rainbow trout, chinook salmon, chum salmon and keta

virus (ASPV) and the salmon gill poxvirus (SGPV). In both

salmon. Clinical outbreaks usually occur 5 to 9 months after

cases, the mechanism by which they adversely affect the

the transfer of young salmon (smolts) to the sea. In recent

host and their contribution to gill pathology is not clear. The

years it has been associated with heart and skeletal muscle

ASPV was first isolated from Atlantic salmon in 1955 in Nor-

inflammation (HSMI) (Wessel et al., 2012).

way. The SGPV was first observed in 2006 in Norway by

Heart and skeletal muscle inflammation (HSMI) has been reported in the Norwegian industry since 1999. The general pathological findings of HSMI indicate circulatory failure, and the characteristic histopathological findings are epi-

electron microscopy in the gills of Atlantic salmon that suffered from a proliferative disease. Poxvirus-infected epithelial gill cells exhibit extreme hypertrophy and degeneration of the nucleus.

carditis, endocarditis, myocarditis, myocardial necrosis, red skeletal myositis and necrosis. The morbidity and mortality rates in outbreaks of HSMI can reach 100 % and up to 20 % respectively (Kongtorp et al., 2004).

Since its discovery in 1999 in Norway, HSMI has spread to Scotland, the United Kingdom, Chile, and Canada. Although HSMI was formally diagnosed only in Atlantic salmon (Fig. 6), other salmonids and some marine fish have been shown to be susceptible to infection by PRV.

BACTERIAL DISEASES Most pathogenic fish bacteria are gram-negative, but within gram-positive bacteria, the most important is Renibacterium salmoninarum.

Many of the bacteria that affect salmon cause septicaemia, since they are distributed to the animal’s organs through the bloodstream.

Bacteria infect salmon through the gills, gut and skin. Table 2 shows the main bacterial diseases affecting farmed salmon.

Figure 6. Atlantic salmon with heart and skeletal muscle inflammation.

Image courtesy of Marcos Godoy.

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