Susceptibility to furunculosis

Most fish species would appear to be susceptible to infections by A. salmonicida, but the level of susceptibility is variable. For example, among salmonids, susceptibility to infection is reported to be low in rainbow trout (Cipriano and Heartwell, 1986; Pérez et al., 1996), while brook trout, brown trout and many other salmon species appear to have a high susceptibility (McCraw, 1952; Evelyn, 1971; Klontz and Wood, 1972; Miyazaki and Kubota, 1975; McCarthy, 1977a; Cipriano and Heartwell, 1986; Austin and Mcintosh, 1988). In addition, susceptibility may vary within the same fish species raised from different genetic lines (Dahle et al., 1996; Marsden et al., 1996) or with different histories of exposure to A. salmonicida (St Jean, 1992). Because of the potentially inheritable nature of some disease resistance, directed breeding programmes aimed at raising stocks inherently resistant to furunculosis have been investigated as a possible disease-control strategy in salmonids (Gjedrem et al., 1991; Lund et al., 1995; Gjedrem, 1997) and non-salmonids (Sovényi et al., 1988; Hjeltnes et al., 1995). However, the multifactorial nature of inheritable characteristics complicates selective breeding programmes and much work remains to be done in this area (Gjedrem, 1997). Species susceptibility to infection by atypical A. salmonicida is discussed in a later section.

Among salmonids, susceptibility to furunculosis may also be age-related. Many early workers in furunculosis research believed that, in wild salmonid populations, furunculosis was mainly a disease of older fish (Plehn, 1911; Mettam, 1915; McCraw, 1952). Although this perception may, in part, have been due to the easier observation of large carcasses in rivers, experimental evidence did suggest that young fish (under 1 year old) are relatively resistant to A. salmonicida infections (Blake and Clarke, 1931; Mackie and Menzies, 1938; Scallan, 1983). The mechanisms of resistance in young fish are essentially unknown but are probably non-specific (Krantz and Heist, 1970). Furthermore, not all workers agree that age plays a significant part in susceptibility to furunculosis (McCarthy, 1977a; Inglis et al., 1993). McCarthy and Roberts (1980), referring to the disease in fingerlings, observed that fish of this size contract an acute form of the disease, which results in rapid death with little more than slight exophthalmos. Mortalities in infected fish in the 0+ age group

Table 10.1. Salmonid fish species from which typical Aeromonas salmonicida has been isolated (after Bernoth, 1997a).

Fish species

--History of

Common name Scientific name Habitat isolation Reference

Table 10.1. Salmonid fish species from which typical Aeromonas salmonicida has been isolated (after Bernoth, 1997a).

Atlantic salmon

Salmo salar

Fresh water

Covert*

McCarthy (1977a)

Clinical

Bernoth (1997a)

Sea water

Clinical

Smith (1997)

Amago salmon

Oncorhynchus rhodurus

Sea water

Clinicalt

Miyazaki and Kubota (1975)

Brook trout

Salvelinus fontinalis

Fresh water

Covert

Bullock and Stuckey (1975)

Clinical

Jensen (1977)

Brown trout

Salmo trutta m. lacustris

Fresh water

Covert

Jensen and Larsen (1980)

Clinical

Mackie etal. (1930)

Chinook salmon

Oncorhynchus tshawytscha

Not specified

Not specified?

Fuller etal. (1977)

Chum salmon

Oncorhynchus keta

Fresh water

Covert

Nomura etal. (1993)

Clinical

Sakai and Kimura (1985)

Sea water

Clinical

Wiklund etal. (1992)

Coho salmon

Oncorhynchus kisutch

Fresh water

Clinical

Wiklund etal. (1992)

Cutthroat trout

Salmo clarki

Fresh water

Not specified

McCarthy (1975)

Dolly Varden

Salvelinus malma

Fresh water

Not specified

McCarthy (1975)

Japanese char

Salvelinus leucomaenis

Not specified

Clinical

Sakai and Kimura (1985)

Lake trout

Salvelinus namaycush

Fresh water

Covert

Daly and Stevenson (1985)

Clinical

McCarthy (1975)

Masu salmon

Oncorhynchus masou

Fresh water

Covert

Nomura etal. (1993)

Pink salmon

Oncorhynchus gorbuscha

Fresh water

Covert*

Nomura etal. (1993)

Clinical

Sakai and Kimura (1985)

Pollan

Coregonus pollan

Fresh water

Not specified?

McCarthy (1975)

Rainbow trout

Oncorhynchus mykiss

Fresh water

Covert

Bullock and Stuckey (1975)

Clinical

Jensen (1977)

Sea water

Clinical

Fernandez etal. (1995)

Sea trout

Salmo trutta m. trutta

Fresh water

Covert

Hirvelä-Koski etal. (1988)

Clinical

Mackie etal. (1935)

Sockeye salmon

Oncorhynchus nerka

Not specified

Clinical

Sakai and Kimura (1985)

* Apparently healthy fish not showing signs of infection (see Hiney eta/., 1997b). TNot specified whether typical or atypical A. salmonicida but assumed to be typical.

* Apparently healthy fish not showing signs of infection (see Hiney eta/., 1997b). TNot specified whether typical or atypical A. salmonicida but assumed to be typical.

Table 10.2. Freshwater non-salmonid species from which typical Aeromonas salmonicida have been isolated (after Bernoth, 1997a).

Fish species

Table 10.2. Freshwater non-salmonid species from which typical Aeromonas salmonicida have been isolated (after Bernoth, 1997a).

Fish species

Common name

Scientific name

History of isolation

Reference

American eel

Anguilla rostrata

Clinical

Noga and Berkhoff (1990)

Brassy minnow

Hybognathus hankinsoni

Unclear*

McFadden (1970)

Brook stickleback

Culaea inconstans

Unclear

McFadden (1970)

Carp

Cyprinus carpió

Clinical

Mackie et al. (1930)

Unclear

Bernoth (1997b)

Catfish

Silurus glanis

Clinical

Mackie eta/. (1930)

Chestnut lamprey

Ichthyomyzon castaneum

Unclear

Bernoth (1997a)

Common shiner

Notropis cornutus

Clinical

Ostland eta/. (1987)

Creek chub

Semotilus atromaculatus

Clinical

Ostland eta/. (1987)

Unclear

McFadden (1970)

European eel

Anguilla anguilla

Incidental

Slack (1937)

Fathead minnow

Pimephales promelas

Clinical

McFadden (1970)

Goby

Cottus gobio

Clinical

Bernoth (1997b)

Golden shiner

Notemigonus crysoleucas

Clinical

Ostland et al. (1987)

G roper

Roccus mississippiensis

Unclear

Herman (1968)

Lamprey

Not specified

Not specifiedt

McCarthy (1975)

Minnow

Phoxinus phoxinus

Unclear

Bernoth (1997a)

Mottled sculpin

Cottus bairdi

Incidental

Rabb and McDermott (1962)

Non-salmonids

Incidental

Bragg (1991)

Northern pike

Esox lucius

Clinical

Bernoth (1997a)

Ornamental cyprinids

Unclear

Bernoth (1997a)

Paddlefish

Polyodon spathula

Clinical

Ford etal. (1994)

Red belly dace

Chromomus eos

Clinical

McFadden (1970)

Smallmouth bass

Micropterus dolomieui

Clinical

Le Tendre etal. (1972)

Stickleback

Gasterosteus aculeatus

Unclear

Barker and Kehoe (1995)

Tench Tinea tinea Clinical Mackie et al. (1930)

CovertT Bernoth and Körting (1992)

White sucker Castostomus commersoni Clinical Ostland et al. (1987)

Yellow bass Morone mississippiensis Clinical Buckley (1969)

Yellow perch Perca flavescens Unclear McFadden (1970)

""Unclear from history whether isolation was from a clinical case or was an incidental finding. TNot specified whether typical or atypical A. salmonicida but assumed to be typical.

Table 10.3. Marine non-salmonid species from which typical Aeromonas salmonicida have been isolated (after Bernoth, 1997a).

Fish species

- History of

Common name Scientific name isolation Reference

Table 10.3. Marine non-salmonid species from which typical Aeromonas salmonicida have been isolated (after Bernoth, 1997a).

Fish species

- History of

Common name Scientific name isolation Reference

Atlantic cod

Gadus morhua

Incidental

Willumsen (1990)

Coalfish

Pollachius virens

Incidental

Willumsen (l990)

Cuckoo wrasse

Labrus bimaculatus

Clinical

Treasurer and Cox (1991)

Goldsinny wrasse

Ctenolabrus rupestris

Clinical

Treasurer and Laidler (1994)

Rock cook

Centrolabrus exoletus

Clinical

Treasurer and Laidler (1994)

Sea bream

Sparus aurata

Clinical

Real et al. (1994)

Striped trumpeter

Latris lineata

Incidental

Bernoth (1997a)

Surf smelt

Thallichthys pacificus

Unclear*

Schiewe et al. (1988)

Turbot

Psetta maxima

Clinical

Nougayrede et al. (1990)

Scophthalmus maximus

Clinical

Toranzo and Barja (1992)

Wrasse

Labridae

Clinical

Treasurer and Cox (1991)

*Unclear from history whether isolation was from a clinical case or was an incidental finding.

*Unclear from history whether isolation was from a clinical case or was an incidental finding.

can be high and have been reported to reach 93% to 40% during the egg to smolt stages (St Jean, 1992). In the experience of these authors, furunculosis can occur in Atlantic salmon alevin whose yolk sacs are still attached.

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