Dr. Duane Barker of the Centre for Aquaculture and Seafood Development (C-ASD) at Memorial's Marine Institute might just be on the verge of discovering the cure for the common cod. Dr. Barker and C-ASD recently completed several research projects funded by the National Research Council - Industrial Research Assistance program (NRC-IRAP), that focus on potential diseases of cultured Atlantic codfish, one of which will investigate whether or not the use of immunostimulants can boost fish health. The stimulants are similar to echinacea for humans.
"The use of oral immunostimulants is a safe, chemical-free method of promoting fish health," Dr. Barker explains. "Its use is gaining popularity for salmon farming in the United Kingdom and catfish farming in the Southern United States."
Despite the fact that cod aquaculture has been given a priority for development in Newfoundland, the industry is still relatively new. Research on the immune system of hatchery-reared cod is in its infancy.
Here's what is known: common fish-farming procedures such as grading, handling and transfer can be very stressful to cultured fish. Changes in water chemistry (oxygen, temperature, salinity, ammonia, etc.) and predators near a sea-cage can also be traumatic. When fish are stressed, chemicals released into their blood reduce the ability of the immune system to function efficiently. Consequently, fish may become susceptible to diseases.
To compound this, Dr. Barker says, "a debate currently exists as to whether or not hatchery-reared fish receive the appropriate stimuli during development." This could mean that their immune system is not as effective as that in wild fish.
The drawbacks of vaccination
Traditionally vaccines have been the method of choice for boosting a fish's immune system. However, some methods of administration (e.g., injection) can be quite laborious, costly and highly stressful to the fish. Most commercial vaccines usually enhance resistance to only one or two specific pathogens, and confer only a temporary resistance to disease. (Immunostimulants, by contrast, can boost immunity to a variety of pathogens, thus are non-specific.) Another vaccine drawback: most existing commercial vaccines have been designed from studies on salmonids held in freshwater.
Dr. Barker's study involves 130 juvenile cod (divided among 10, 120L tanks with 13 cod/tank) being held at the aquaculture facility of C-ASD. During an initial 2-week acclimation period, all cod were fed daily using a commercial pellet feed with a recommended dose of 1.0 % body weight per day. After this 2-week period, immunostimulants were added to the feed and administered for an additional 2-week period. The recommended feeding protocol is two weeks with immunostimulants and six weeks on regular feed. Two tanks were used for each immunostimulant (total 8) and an additional 2 tanks will serve as a reference (control), receiving only the commercial feed (immunostimulant-free). The immunostimulants will be evaluated (bi-weekly) by comparing their effectiveness in helping remove a parasite infection and improving cod growth.
It is expected that results from Dr. Barker's pilot study will set the baseline for future, long-term studies using cultured cod.
All four tested products were effective to some extent, but two of the four showed very promising results, demonstrating the highest growth rates and lowest feed conversion ratios (FCR's). In addition, those cod fed immunostimulants had a significant reduction (24-38% decrease) in parasite infections. Conversely, parasite infections increased (>50%) among the control groups (not fed immunostimulants). The experimental cod used for the projects were donated by Mr. Andy Walsh of Northern Cod Ventures Ltd.
If cod have a much different immune response than salmon, as recent studies suggest, research on immunostimulants will be critical to their commercial development as vaccines for salmon may not be effective. The importance of these oral immunostimulants cannot be over-emphasized. These products do not contain any medications or chemicals, thus there have no harmful effects on the consumer or environment. Furthermore, at current prices of $205 (CDN) per tonne of immunostimulant product (to be mixed at 8g/kg of feed), this seems to be a relatively inexpensive fish health improvement cost. The next step involves further research to develop an effective protocol and feed concentration that can be used at key times in the commercial production of cod.
Step two in this research will be soon underway as Dr. Barker has recently been awarded funding from AquaNet and the Atlantic Innovative Fund (AIF). These agencies have agreed to fund this research, which also includes a graduate student stipend, for 3 years beginning this summer. The initial experiments will be conducted in the aquaculture facility of C-ASD and eventually tests will be conducted at sea cages with the cooperation of the industry partners Northern Cod Ventures and Northern Aquaculture Corporation.
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