Fishing with Rod Discussion Forum

Please login or register.

Login with username, password and session length
Advanced search  

Author Topic: Greasy fish farms releasing infected blood water  (Read 1261 times)

Fisherbob

  • Old Timer
  • *****
  • Offline Offline
  • Posts: 1069
Re: Greasy fish farms releasing infected blood water
« Reply #30 on: December 05, 2017, 03:29:55 PM »

Here's some reading on PRV

http://www.dfo-mpo.gc.ca/science/aah-saa/species-especes/aq-health-sante/prv-rp-eng.html
  Thanks Dave. It looks like PRV has been around a lot longer then salmon farming. The only new thing is the abilaty to detect it. :)
Logged

GordJ

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 154
Re: Greasy fish farms releasing infected blood water
« Reply #31 on: December 05, 2017, 05:01:39 PM »

But I still donít know how it is spread, just where. I understand it isnít in eggs but I couldnít find how it is transmitted.
Logged

Dave

  • Old Timer
  • *****
  • Offline Offline
  • Posts: 2816
Re: Greasy fish farms releasing infected blood water
« Reply #32 on: December 05, 2017, 06:52:43 PM »

But I still donít know how it is spread, just where. I understand it isnít in eggs but I couldnít find how it is transmitted.

Just did a quickie search and found this interesting read.  Transmission is about 1/2 way in

https://thefishsite.com/articles/piscine-reovirus-prv-an-underestimated-pathogen-in-the-scottish-salmon-industry
Logged

GordJ

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 154
Re: Greasy fish farms releasing infected blood water
« Reply #33 on: December 05, 2017, 07:21:30 PM »

Yes, but it says that it isnít transmitted through reproduction and it doesnít seem to find how it is. It seems to me that how it is transmitted should be important to anyone trying to protect fish.
Logged

Dave

  • Old Timer
  • *****
  • Offline Offline
  • Posts: 2816
Re: Greasy fish farms releasing infected blood water
« Reply #34 on: December 05, 2017, 08:17:12 PM »

I thought it was transmitted vertically but someone correct me if I'm wrong.
Back when I did that stuff we disinfected our Cultus sockeye eggs in an iodine based liquid to kill viruses.  Pretty sure it is standard hatchery procedure everywhere. Back then the bad virus was IHNv and this product was said to kill it.  My guess is it will kill PRV as well, and I would be surprised if salmon farmers did not use this relatively cheap and effective method to disinfect their eggs at their hatchery.

This would of course mean the fish being transferred to net pens (what the most recent fuss is all about) would be PRV free or would have picked it up from another source.  Iím sure Iíve oversimplified this but it seems easy enough to test.
Logged

Easywater

  • Old Timer
  • *****
  • Offline Offline
  • Posts: 883
Logged

shuswapsteve

  • Old Timer
  • *****
  • Offline Offline
  • Posts: 890
Re: Greasy fish farms releasing infected blood water
« Reply #36 on: December 05, 2017, 11:04:55 PM »

d
so this virus does cannot cause disease that can kill salmon? please clarify.

Itís been a matter of debate for awhile. Although PRV is strongly correlated to HSMI it doesnít necessarily result in disease. The mode how it actually can causes disease is not entirely clear. PRV is ubiquitous in farmed Atlantic salmon, but they all donít get HSMI just because they have PRV.  If you read the literature on it you will find that Atlantic salmon can have high concentrations of PRV but never develop signs of HSMI. Other research has shown that wild salmonids from here to Alaska have likely had PRV since the 70s. Wild salmonids here in B.C. have been shown to have PRV but show no clinical signs of HSMI.

Researchers here in a recent study (Kyle Garver is the scientist who with other researchers looked into this) injected wild salmon with PRV and held them for several weeks and none developed HSMI. Recent work shortly afterwards with Kristy Miller did find what they believe was HSMI on this one farm under study. The authors from that study believe that HSMI could have been missed before during routine sampling of morts because the window when it occurred is not very obvious with current techniques. One also has to understand that this particular farm was heavily studied so the likelihood to find HSMI was much better. Obviously, itís not practical to conduct an intensive study like this on each fish farm to find HSMI, but likely better diagnostic technology will be adopted that doesnít require a research team to spend a whole year studying one farm.

Itís important to note that the presence of HSMI has only been found in farmed Atlantic Salmon - not wild Pacific Salmon. Even in Norway, where this is apparently a big problem according to industry critics, there is no evidence that wild salmon there have HSMI. So far, this has been found in farmed Atlantic Salmon. Not very surprising as most fish health work has been with cultured fish including those in aquaculture. Doing fish health work on wild salmon comes with challenges. It is thought that the quality of fish husbandry in aquaculture can influence whether HSMI develops or not.  This makes sense considering that stress and environmental factors are known to leave the host more vulnerable to disease.  So, when I see a media article that says PRV is deadly to wild salmon I have to ask the question where is this evidence. It doesnít mean that it canít impact wild salmon, but theories of what PRV is doing to wild salmon doesnít equate necessarily to fact unless it can be demonstrated and documented.
Logged

GordJ

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 154
Re: Greasy fish farms releasing infected blood water
« Reply #37 on: December 06, 2017, 07:21:52 AM »

I thought it was transmitted vertically but someone correct me if I'm wrong.
Back when I did that stuff we disinfected our Cultus sockeye eggs in an iodine based liquid to kill viruses.  Pretty sure it is standard hatchery procedure everywhere. Back then the bad virus was IHNv and this product was said to kill it.  My guess is it will kill PRV as well, and I would be surprised if salmon farmers did not use this relatively cheap and effective method to disinfect their eggs at their hatchery.


ďA study following Norwegian broodstock and progeny from 2008 to 2011 found that PRV was not isolated from eggs collected from broodstock with a high PRV prevalence, suggesting vertical transmission (from fish to egg) is unlikely to play a major role in PRV spread.Ē
Quoted from the study mentioned previously.
« Last Edit: December 06, 2017, 07:24:13 AM by GordJ »
Logged

RalphH

  • Old Timer
  • *****
  • Offline Offline
  • Posts: 1956
Re: Greasy fish farms releasing infected blood water
« Reply #38 on: December 06, 2017, 07:28:32 AM »

Thanks for that Steve.

With recorded mortality rates as high as 20% it isn't beyond bounds to describe the disease as deadly. Mortality rates of up to 20% is within the range of serious human diseases like smallpox and cholera. Does the recorded mortality rate include mortality where the disease is a secondary cause such as predation or is it based? Could it effect other important aspects of the salmon life cycle like reproductive efficiency?

Many disease viruses can lay dormant in a host and not cause disease so PRV isn't unusual in this sense either.

One thing that is lacking in the claim the virus was in the fish processing plant effluent is the concentration of the virus (ie the same or close to the same as the surrounding water or much higher?) and were the viruses alive.
 
Logged
"Never force conversation on a stranger. They are probably there just to fish and find solitude. If you ask a question or 2 and receive only answers...and no attempt to keep the conversation going, gracefully follow the implied suggestion and leave the angler alone"
               from " Courtesy and Safety"; Morris and Chan on Fly Fishing Lakes by Brian Chan and Skip Morris

aquapaloosa

  • Old Timer
  • *****
  • Offline Offline
  • Posts: 642
  • They don't call'em fish for nothin.
Re: Greasy fish farms releasing infected blood water
« Reply #39 on: December 06, 2017, 08:14:56 AM »

I would add that in Garvers study he also injected cultured atlantic salmon with prv and found the same results as with the pacific species.  This PRV virus found in the NW pacific has been found as far up as alaska and is  genetically different from the PRV in Norway by 20%.
Logged
Chicken farm, pig farm, cow farm, fish farm.