Nodaviruses are microscopic, single
stranded RNA viruses. There are lots of different varieties but all are members of the
family Nodaviridae. Nodavirus cause a disease known as “VNN” (Viral Nervous
Necrosis). This disease typically affects newborn baby fish, if you see the little
critters swimming around disorientated, swimming in spirals, chasing their tails or
belly up then you have a problem. This disease is a big problem for the aquaculture
industry as fish are susceptible to mass infections by this virus. This is especially
a problem for fingerlings that can suffer from nodavirus infection and then up to 100%
mortality. Nodavirus generally infect the fish’s brain, eyes and spinal cord and can
be seriously dangerous to juvenile fish but not such a problem for larger fish which
may be infected but show no outward sign of disease. Nodaviruses are quite common in
dozens of different marine species worldwide and large adult fish can be carriers of
this disease but otherwise healthy.
In Australia the Barramundi industry is the one that has had the most problem in the
past as Barras are very susceptible to this disease. Most of the Barra Hatcheries have
experienced Nodavirus outbreaks in the past despite all the best efforts to remove the
potential for this problem. It’s a real battle that has been waged with a vengeance
for the last 15 years and, despite a phenomenal amount of research and knowledge gained
on the viruses, we are winning the war but still losing battles along the way. The
continuing intermittent outbreaks of nodavirus in different hatcheries Australia-wide
is a concern that needs to be addressed. This was brought to the fore in 2004 when a
Nodavirus outbreak occurred in a NSW hatchery.
In NSW the NSW DPI has always had strict regulations relating to Barramundi due to
the high incidence of nodavirus infections in the past and potential for it to occur
again in the future. These regulations are designed to not only protect the aquaculture
industry but also protect the wild fish stocks from infection.
Now with the outbreak in another species Australian Bass (Macquaria novemaculeata)
a new battlefront has opened in NSW and a new campaign by NSW DPI is being waged to
fight this problem. This is
especially important because fish produced in this hatchery are used for restocking
back into the wild. N.S.W. DPI has a mandate to protect the environment and the wild
species of fish as well as the aquaculture industry and this is being reflected in the
new HQAP (Hatchery Quality Assurance Program) and the new Nodavirus Testing Program.
The nodavirus testing program has been instigated for all Australian Bass hatcheries
that supply bass for restocking into the wild.
Nodavirus is a disease that is hard to identify. In Australian Bass there are no
absolute clinical signs to watch for in infected bass fingerlings. Generally its larval
fish in the first month of life that are the most susceptible to nodavirus. You may
notice a lack of appetite followed by the typical spinning swim behaviour, these would
be the main symptoms to watch out for. I have heard rumours of extra shiny silver eyes
but even healthy fish can show that so not sure if relevant. Another symptom I have
heard is over-inflated swim bladders. If you see any or all of these symptoms in your
juvenile fish then within 2 weeks, if it's nodavirus, all your fish may be dead. This
is a notifable disease so get in touch with NSW DPI if you suspect a problem.
The only good news is that from what I can gather it is only marine fish that to
date are known to suffer from this disease. Nodavirus infections don’t seem to occur
in freshwater fish. Bass broodstock sourced from freshwater areas should be nodavirus
free. The trouble arises that you need to breed them in salt water and the water itself
can be the cause of infection.
The battle against nodavirus continues in NSW so be aware and on guard.
Nodavirus Testing Program in NSW (NTP) & at Aquablue 2006/7
Back in 2004 a Nodavirus outbreak occurred in a NSW hatchery. This has lead to
a change in the management procedures for all Australian Bass hatcheries in NSW that
supply bass for restocking into the wild. Aquablue has an Australian Bass hatchery that
is in full production at the moment so this is very important to us.
In 2005 the Nodavirus Testing Program (NTP) was started. All Australian Bass
Hatcheries that are involved in the Dollar for Dollar scheme or supply bass for
stocking into the wild need to register in the NTP. This program involves the hatchery
operators taking blood samples from their bass broodstock after breeding. Samples are
sent to the Virology Laboratory at Elizabeth Macarthur Agricultural Institute, Menangle
NSW for testing for Nodavirus. Additionally at 21 days old 1000 bass larvae from each
batch are also sent in for testing.
This testing program is at no cost to the private hatcheries, it is currently being
paid for by NSW DPI with assistance from money allocated from the recreational fishing
trust. This is money raised from fishing licenses and, as the fish being produced in
the hatcheries are going out for restocking into the wild for recreational fishing,
it's natural that some of this money is used to protect those fish stocks.
This is the third year of the testing program, it started in 2005 with both the
private hatcheries and the NSW DPI’s Port Stephens Fisheries Centre participating. For
year the Nodavirus test results were negative from all hatcheries. Both broodstock
blood samples and larval samples were tested using a mixture of PCR (Polymerase Chain
Reaction), virus isolation and histology techniques. Testing was also conducted on fish
species captured from the wild in the coastal estuaries of NSW. The results were quite
surprising with fish such as luderick and mullet showing a positive result. Positive
adult fish showed no clinical signs of infection and infection rates were less than 5%
which is very low.
Once again this year all hatcheries supplying fish for restocking will be involved
in the nodavirus screening. Aquablue Seafood’s Australian Bass Hatchery does nodavirus
testing, the whole process is quite painless and just another chore that needs to be
done. We are happy to do it as it ensures that the fish we send out and you get are
the best and healthiest. If you need more information just contact Mr Bill Bardsley at
Port Stephens Fisheries Centre 02 4916 3870. Bill’s great, he came out to Aquablue and
showed us exactly what we had to do to get a blood sample. Basically after you have
bred with the fish and remove them from the breeding tank we knock them out and take a
blood sample from the tail section of the bass. We got supplied with a kit free of
charge that has all you need to do the job. NSW DPI supplies a kit free to everyone
involved in NTP. Once the fish is knocked out you put on some new gloves for every fish
you do to avoid contamination and use the needles supplied to take one ml of blood from
the tail region of each fish. Bill came out and showed us exactly where and how to take
the samples so that the fish is unstressed and uninjured. You then place this blood in
the vials supplied in the esky supplied with the ice bottles supplied, and send them to
the lab by the courier that they are paying for. All very straight forward and
Then, after or if the eggs hatch and you get larvae some 21 days later, you scoop up
and send in a 1000 of them for testing. So far all the results have been negative and
let’s hope they stay that way. At Aquablue we are doing everything possible to ensure
that any diseases are never a concern and the fish we sell are the best that you can