Aquaculture - Current Topics

All salmon, like all other living organisms, are at risk of sickness and disease from a variety of sources. This is true of salmon in either the wild or cultured environment. Many strides have been taken to better understand and prevent these diseases, but disease still occurs.

It is important to keep in mind that disease is only one of many possible causes for the decline of fish stocks. Other possible influences include changes in the ocean climate, historic over- harvest or alterations to habitat spawning grounds.

There are many reasons why fish become susceptible to disease: fluctuations in water temperature, water level or salinity, natural physiological changes that mature salmon undergo when migrating from salt to fresh water, abundance of populations, or a combination of factors. Maintaining the healthiest and most disease-free environment for fish, either wild or cultured, is a definite goal for government, environmentalists and aquaculturalists alike.

The only diseases detected on salmon farms in BC are those which are found naturally in wild BC salmon populations. Diseases that pose a risk to the industry, such as sea lice or Infectious hematopoietic necrosis (IHN) were identified before salmon farms arrived in our coastal waters. There is no evidence to indicate that disease outbreaks at salmon farms have resulted in any increase in diseases in wild salmon. In fact, research indicates that farmed salmon are at a higher risk of contracting a disease from wild fish than vice versa.

Fisheries and Oceans Canada works cooperatively with the Province of of BC and the aquaculture industry to continually modernize our policies and regulations with respect to fish health management.

Strict regulations and rigorous screening protocols minimize the risk of an introduction or transfer of disease. The Department’s eggs-only policy has been very effective in minimizing the risks associated with disease transfer. Under the Fisheries Act, the Fish Health Protection Regulations control the importation and movement of live fish and eggs within Canada. Both DFO and the Province of BC are committed to a national aquatic animal health program to prevent diseases from being introduced into BC fish production – either through salmon enhancement programs or aquaculture. Live smolts used for rearing are prohibited from being imported to British Columbia and strict regulations govern the importation of eggs to prevent the spread of disease.

Most eggs are now generated in BC and only eggs from hatcheries participating in a disease-free certification program defined by Canadian Fish Health Protection regulations may be imported. These eggs must go to a certified BC hatchery where they are quarantined, surface disinfected and screened for disease in the hatchery. Young fish are then grown in disease-free hatchery water. After the young salmon are transferred to saltwater net pens, however, they may be exposed to naturally-occurring disease pathogens in the marine environment or from passing wild fish. Some may contract diseases and require treatment.

Disease issues were carefully studied in the BC Salmon Aquaculture Review in 1997 and the Scientific Panel recommended further research. To expand our understanding of the threat from disease and provide better prevention against disease outbreaks, the Province of BC and the Government of Canada continue to research the variety of diseases, sources of diseases, how diseases are transferred and potential treatments. This information benefits a sustainable aquaculture industry and assists salmon enhancement facilities (hatcheries) increase production, ensure greater survival of returning wild stocks and reduce the impact these wild stocks may have on introducing disease to other wild stocks or fish farms.

Sea lice are present in the marine environment and are found naturally on many species of fish, most commonly pink and chum salmon. BC salmon farms are neither significantly impacted by sea lice nor lay as a root cause for sea lice outbreaks on wild stocks. As mentioned earlier, sea lice infestations were recorded by DFO decades before salmon aquaculture was introduced to BC.

There are many factors that are likely to be a cause of an increase in the appearance of sea lice. Infestations of sea lice can increase very rapidly if conditions are favourable to the lice. Some citizens in the Broughton Archipelago area expressed concern of a potential sea lice outbreak to DFO’s attention earlier this summer. This year, water temperatures during the last two months and especially the high salinity, due to low, fresh water run-off, created a suitable environment for sea lice. Infestation rates also tend to be higher if there are higher densities of fish. Due to record returns of adult Pink salmon into rivers flowing into the Broughton Archipelago area last year, numbers which we have not seen in the last 50 years, it is logical to expect a record number of juveniles.

Because density of juveniles is high, the infection rate is likely to be high. DFO conducted a two-pronged approach to assess levels of sea lice on juvenile salmonids in a timely and effective manner. Data from preliminary results from a trawl survey, conducted June 29th and July 4th in the in the Broughton Archipelago area did not demonstrate a significant sea lice infestation of pink salmon in the survey area. Data from a second survey using seine sampling conducted in the Broughton Archipelago and Queen Charlotte Strait areas July 6-9 (following the natural migration route of juvenile pinks to the ocean), also did not demonstrate the infestation levels alleged by some residents in the Central Coast area. A full report based on the analysis of both surveys will be ready later this fall.

I’ve heard a lot about disease affecting aquaculture sites in Norway – could this happen in BC?

The example of Norway is interesting because its root cause was a salmon enhancement program and not a result of actions by the aquaculture industry. Diseased salmon from Sweden were imported into Norway as part of an enhancement program and the aquaculture industry was the unfortunate victim in this case. Strict Canadian regulations and protocols mentioned above should preclude this incident from happening in BC.