| There
has been little research conducted on the significance of viral infections
in freshwater crayfish. Many of the viruses listed above have been described
following their detection in a small number of animals, in some cases
only one animal. A lack of importance should not be inferred from our
poor understanding of these pathogens. Experiences in other aquaculture
industries, including shrimp, would suggest that viruses will be important
to manage as freshwater crayfish aquaculture industries develop. Viral
diseases have caused US$billions of losses in shrimp aquaculture since
the early1990s. Furthermore, viruses are likely to be important pathogens
of natural freshwater crayfish populations. |
| |
| From
this very limited knowledge base, it is difficult to speculate which of
the viruses known to infect freshwater crayfish are likely to be the more
significant. Due to their very wide occurrence, both geographically and
within populations (eg. frequently 100% of noble crayfish populations
are infected with AaBV), it is unlikely that the intranuclear bacilliform
viruses which infect the gut of freshwater crayfish are highly pathogenic
to their normal host species. Nonetheless, even pathogens with low virulence
may be associated with other detrimental effects, such as growth retardation
as is the case of CqBV. Infection by WSSV causes serious mortality in
the procambarid and astacid crayfish that have been tested. The affect
of WSSV infection on Australian species (which are all parastacids) has
not been thoroughly studied. Preliminary transmission trials with WSSV
have shown that Cherax quadricarinatus (redclaw) are susceptible
to infection but do not become diseased (Lightner, pers. comm.), and field
observations from South America where WSSV is now common in shrimp suggest
that redclaw are not highly susceptible to disease. There is nothing known
about the susceptibility of other Australian species. For more information
on WSSV (as well as other shrimp diseases), download
the AQIS draft import risk analysis on shrimp (I was the principle author
of this report). |
| |
| Most
of the other viruses have been found in moribund crayfish, in the absence
of other serious pathogens, suggesting that they are capable of
causing mortality in the species from which they were described.
Of significance to the aquaculturist, CGV has been associated with mortality
of up to 85% 8 weeks after C. quadricarinatus juveniles have hatched
from eggs. It is therefore likely that CGV is partly responsible for occasional
reports of poor survival of C. quadricarinatus juveniles in tanks
or poor juvenile production in ponds. |
| |
| There
are no cures for viral infections in crustaceans so the best way to manage
them is by avoidance. In shrimp aquaculture, a very high importance is
placed on obtaining stock free from viral pathogens. For shrimp that is
often difficult as the major pathogens, such as WSSV, yellow head virus,
Taura syndrome virus, hepatopancreatic parvovirus and the baculoviruses,
are frequently widespread. Moreover, many shrimp aquaculture industries
rely heavily on catching broodstock from the wild. Shrimp aquaculture
therefore relies heavily on sophisticated and expensive diagnostic tests
for producing virus-free animals for stocking. Crayfish culture has an
advantage from this perspective. The freshwater crayfish lifecycle is
effectively closed in the farm system that is, crayfish are easily bred
in captivity and there is no need to continually catch from the wild broodstock
which may be infected with viruses. Of the crayfish viruses, only CqBV
and CGV have been studied in any depth regarding transmission. Both are
transmitted via the oral route, ie. by the crayfish feeding on infected
tissue or particulate matter which has virions attached to it. Virus-free
C. quadricarinatus juveniles have been produced in a small-scale
hatchery by stripping eggs from females, and incubating and growing the
eggs and juveniles, respectively, in clean water. As it is relatively
rare for a crustacean pathogen to be transmitted within eggs, it is likely
that specific pathogen-free (SPF) juvenile crayfish of all species can
be produced in this manner. Of course, broodstock is not the only source
of virus introduction to aquaculture systems. Other sources include the
water supply, other potential hosts in the nearby environment (such as
feral crayfish species, other crustaceans or even insects may carry pathogens
which can infect freshwater crayfish) or feed (as discussed above for
WSSV). The use of SPF stocks, in conjunction with strict quarantine (biosecurity)
controls, is an extremely effective measure to manage viral diseases in
freshwater crayfish aquaculture. |
| References |
| |
| Anderson IG, Shariff M, Nash G, Nash M (1987) Mortalities
of juvenile shrimp, Penaeus monodon, associated with Penaeus monodon
baculovirus, cytoplasmic reo-like virus, and rickettsial and bacterial
infections, from Malaysian brackishwater ponds. Asian Fisheries Science
1: 47-64 |
| |
| Edgerton BF (1996) A new bacilliform virus in Australian Cherax destructor
(Decapoda: Parastacidae) with notes on Cherax quadricarinatus
bacilliform virus (= Cherax baculovirus). Diseases of Aquatic Organisms
27(1): 43-52 |
| |
| Edgerton BF (1996) Viruses of Freshwater Crayfish. PhD Thesis. James Cook
University of North Queensland, Townsville |
| |
| Edgerton BF (1999) A review of freshwater crayfish viruses. Freshwater
Crayfish 12: 261-278 |
| |
| Edgerton BF, Owens L (1997) Age at first infection of Cherax quadricarinatus
by Cherax quadricarinatus bacilliform virus and Cherax Giardiavirus-like virus, and production
of putative virus-free crayfish. Aquaculture 152(1-4): 1-12 |
| |
| Edgerton BF, Owens L (1999) Histopathological surveys of the redclaw freshwater
crayfish Cherax quadricarinatus in Australia. Aquaculture 180(1-2):
23-40 |
| |
| Edgerton BF, Owens L, Glasson B, De Beer S (1994) Description of a small
dsRNA virus from freshwater crayfish Cherax quadricarinatus. Diseases
of Aquatic Organisms 18(1): 63-69 |
| |
| Edgerton BF, Owens L, Harris L, Thomas A, Wingfield M (1995) A health survey
of farmed redclaw crayfish Cherax quadricarinatus (von Martens),
in tropical Australia. Freshwater Crayfish 10: 322-338 |
| |
| Edgerton BF, Paasonen P, Henttonen P, Owens L (1996) Description of a bacilliform
virus from the freshwater crayfish, Astacus astacus. Journal of
Invertebrate Pathology 68(2): 187-190 |
| |
| Edgerton BF, Webb R, Anderson IG, Kulpa EC (2000) Description of a presumptive
hepatopancreatic reovirus, and a putative gill parvovirus, in the freshwater
crayfish Cherax quadricarinatus. Diseases of Aquatic Organisms
41(2): 83-90 |
| |
| Edgerton BF, Webb R, Wingfield M (1997) A systemic parvo-like virus in
the freshwater crayfish Cherax destructor. Diseases of Aquatic
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| |
| Groff J M, McDowell T, Friedman C S, Hedrick R P (1993) Detection of a
nonoccluded baculovirus in the freshwater crayfish Cherax quadricarinatus
in North America. Journal of Aquatic Animal Health 5(4): 275-279 |
| |
| Halder MaAW (1988) Freshwater crayfish Astacus astacus - a vector
for infectious pancreatic necrosis virus (IPNV). Diseases of Aquatic Organisms
4: 205-209 |
| |
| Halder M E (1987) The freshwater crayfish (Astacus astacus) as a
vector of infectious pancreatic necrosis virus. 112 pp |
| |
| Hedrick RP, McDowell TS, Friedman CS (1995) Baculoviruses found in two
species of crayfish from California. Aquaculture ’95, Abstracts. |
| |
| Jones JB, Lawrence CS (2001) Diseases of yabbies (Cherax albidus)
in Western Australia. Aquaculture 194(3-4): 221-232 |
| |
| Lightner DV, Redman RM, Poulos BT, Nunan LM, Mari JL, Hasson KW (1997)
Risk of spread of penaeid shrimp viruses in the Americas by the international
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International des Epizooties 16(1): 146-160 |
| |
| Owens L, McElnea C (2000) Natural infection of the redclaw crayfish Cherax
quadricarinatus with presumptive spawner-isolated mortality virus.
Diseases of Aquatic Organisms 40(3): 219-223 |
| |
| Paasonen P, Edgerton BF, Tapiovaara H, Halonen T, Henttonen P (in press)
Freshwater crayfish virus research in Finland: state of the art. Report
from the Nordic-Baltic workshop on crayfish research and management. Eastern
Norway Research Institute and Estonian Ministry of Environment, Fishery
Dept., |
| |
| Richman LK, Montali RJ, Nichols DK, Lightner DV (1997) A newly recognized
fatal baculovirus infection in freshwater crayfish. Proceedings of the
American Association of Zoo Veterinarians, 1997. Abstracts. |
| |
| Wang Q, White B L, Redman R M, Lightner D V (1999) Per os challenge of
Litopenaeus vannamei postlarvae and Farfantepenaeus duorarum
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170(3-4): 179-194 |
| |
| Wang YC, Lo CF, Chang PS, Kou GH (1998) Experimental infection of white
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DNA
and Putative DNA Viruses