Abstract

Over the last four decades, the growth of salmon farming is arguably one of the greatest success stories of modern aquaculture for a high-value fish species. There have been leaps and bounds in technology, efficiency and quality. This success has not been without the typical boom-and-bust cycles experienced by the industry over the past few years, with the resultant shrinking of margins and global consolidation. The leading farmed salmon producing regions, situated in Chile, Norway, UK, followed by North America, have enjoyed the spectacular success of salmon farming. Other regions, such as Alaska, chose not to embrace aquaculture (finfish farming was made illegal in the early 1990's) in lieu of the history and tradition of a lucrative monopoly of salmon from the wild fisheries. However, what was initially assumed to be a welcomed adjunct to the wild salmon fisheries, has turned into a fierce competitor, with inexpensive, high quality, year-round farmed salmon displacing wild salmon from important marketplaces, especially in Japan. As a result, the value of the Alaskan salmon fishery plummeted from $400 million dollars to $130 million between 1999 and 2002 (Knapp, 2003), resulting in considerable hardship for salmon fishermen and their communities up and down the Alaskan coast.

The Alaskan salmon fishery receives considerable support from Congress to market and differentiate their product from farmed salmon. Much of this effort appears to have gone towards comparisons between food safety and wholesomeness issues, as well as environmental impacts. Often, wild salmon has been portrayed in the media as being: natural in color, lower in organic contaminants, free from antibiotics, and higher in those health-heralded Omega-3 fatty acids, than their cultivated cousins--with the implication that this is different from the farmed salmon product.

Salmon farming has been a boon for aquaculture-oriented veterinarians, as the value of these animals to the producer fosters a demand for the business of high-level clinical medicine. The employment of veterinarians by the salmon farming industry (direct and ancillary) is estimated to be around 300, worldwide (Mitchell, 2004). Not only are the health and welfare of farmed salmon under the purview of veterinarians, but, as food animal production practitioners, the food safety and wholesomeness of their patients is a prime ethical and professional responsibility. Consistently listed as one of the most trusted professions in society, the veterinarian is an important conduit of applied science between the scientific community and the lay-public. It behooves the aquaculture practitioner to be knowledgeable regarding the issues behind the food wholesomeness differences between farmed and wild salmon, and to be able to relate the facts within a politically-charged venue.

This presentation will focus on what is known about four aspects of salmon meat wholesomeness and safety: Colorants, antibiotics, Omega-3 fatty acids, and organic contaminants.

Color

The pink-to-red pigment in the flesh of wild salmonids is obtained only through the diet by the accumulation of the carotenoid astaxanthin (dihydroxycanthaxanthin) (Torrissen, 1986). Another related carotenoid: canthaxanthin (essentially astaxanthin without a couple of hydroxyl groups), is found in smaller quantities in the wild, but has been approved as a food colorant. Both are powerful anti-oxidants, vitamin A precursors, and are implicated in various biochemical functions (favorable influences on fertility and reproduction, Schiedt et al., 1985). Furthermore, carotenoids are known to improve human eyesight and reduce cancer. In the wild, salmon flesh color can vary from white-grey to deep "salmon" color, depending on access to carotenoid containing foodstuffs (algae containing prey and crustaceans). In cultivation, farmers can add astaxanthin and canthaxanthin to the feed and have the luxury of being able to produce a rich, consistent color in the flesh, unlike the variation found in the wild. Due to a concern regarding artificial colors and dyes in our food (e.g., Red Dye No. 40), the Code of Federal Register (21 CFR 101), since 1995, has required the labeling of any food product that contains artificial colors. Although, astaxanthin and canthaxanthin are produced artificially, they are the same molecules as found in the flesh of wild salmon. Salmon farming opponents, however, have forced wholesalers and grocery stores to go by the letter of the law and label farmed salmon packages as having "color added" in order to try and differentiate it from wild salmon. Unfortunately, amongst many consumers, there is a negative connotation implied, not being totally aware of the true nature of carotenoids and salmon. To date, there is no scientific difference in nutritive quality between naturally-obtained carotenoids in wild salmon, versus carotenoids obtained from salmon feed.

Antibiotics

Antibiotics, originally derived from naturally-produced substances from microorganisms, have been a cornerstone of modern medicine, both human and veterinary. Microbial resistance is a phenomenon where microorganisms lose their susceptibility to antibiotic compounds. This is a function of longevity of use, overuse, and non-compliance, and works on a microbial population level, where those microorganisms with innate resistance are selected for. Antibiotic resistance often gets confused with micro-organism virulence, and practitioners should point out that there is no connection. Occasionally, farm animals must be given antibiotics to control bacterial diseases. These antibiotics have been approved by the FDA for the specific indications and animals. Their impact on the environment has been assessed in the registration process, and a specific withdrawal time prior to slaughter has been derived from empirical studies of the pharmacokinetics and pharmacodynamics of the drug, to ensure that no volatile residues or metabolites remain in the flesh of the animal once it reaches the consumer. The cost of antibiotic treatment, together with the loss in flexibility for harvest, is a great incentive for the farmer and the veterinarian, to be extremely judicious in the use of antibiotics. This is no different in fish, where there are currently only two antibiotics available in the US for food fish: oxytetracycline and sulfadimethoxine with an ormetoprim potentiator. There have never been any reported environmental or human-food safety problems from the use of these two compounds in fish.

Omega-3 Fatty Acids

The benefits of Omega-3 fatty acids in our diets are being widely heralded. They have been purported to do everything from reduce the risk for sudden death caused by cardiac arrhythmias; reduce mortalities from coronary heart disease, are antithrombotic, anti-inflammatory, reduce hyperlipidemia, lessen rheumatoid arthritis, and even reduce hypertension (Covington, M., 2004). USDA analysis in 2002 on various sources and species of salmon yielded these values of Omega-3 F.A.'s in grams per 100 gram portion: farmed Atlantic: 2.00; wild Chinook: 1.68; wild Chum: 0.74; wild Coho: 1.50; wild pink: 1.14; wild Sockeye: 1.30.

Organic Contaminants

Polychlorinated biphenyls (i.e., PCB's) and other persistent organic pollutants are halogenated aryl hydrocarbons that exist in virtually all foods, but, being lipophilic, particularly to those with animal fats, such as meat and poultry, dairy products and fish. They are the direct result of past industrial pollution and waste management practices, with their use banned in the US in 1996, which is resulting in a steady decline in the environment and our foodstuffs. Their acute toxicity is very low; however they have been equivocally linked to chronic health problems, including carcinogenicity.

Two papers have concluded, incorrectly, that farmed salmon have higher PCB's than wild salmon (Easton et al., 2002; Hites et al., 2004). Both used the same laboratory in British Columbia, Canada for their analyses.

Easton et al was funded by the Suzuki Foundation, a noted anti-salmon farming group and will be dismissed scientifically because of the small number of samples used (four farmed salmon and four wild salmon) and the statement included in the section 2.3 on Statistical methodology: "As a consequence of the small sample size and the heterogeneous nature of the within-group samples characterized as to contaminant load, no statistical test of this data was done."

Hites et al. (2004), in a "Note" in the journal Science, concluded that: "the consumption of farmed Atlantic salmon may pose health risks that detract from the beneficial effects of fish consumption." The averages of their sample data were: 36.6 parts per billion (ppb) for farmed salmon 4.8 ppb for wild salmon (FDA's tolerance limit is 2000 ppb). All the farmed samples were Atlantic salmon from the major salmon producing areas around the globe, and all the wild samples were various species of Pacific salmon, including: carnivorous high-fat species such as Chinook and coho, and low-fat planktivores Chum and pink salmon. They neglected to sample wild salmon from Puget Sound and wild Atlantic salmon (an 8000 MT fishery) from Europe. They neglected to provide any historical references on past values found in salmon (farmed or wild), which tend to be identical and range from about 25 to 50 ppb. They also failed to provide any context as to the levels in the foods we commonly eat (e.g., butter: 75 ppb; canned tuna: 45 ppb; roasted chicken breast: 32 ppb; fried egg: 19; popcorn in oil: 17 ppb, etc. FDA/Seattle Post-Intelligencer) and neglected to mention that cooking destroys about 50% of the PCB's. Reason's for their unusually low wild salmon levels probably are due to skewing of the sample with low-fat returning chum and pink salmon. There are several curious hints throughout the paper that the authors have an anti-farmed salmon bias, and that these oversights may not have been unintentional.

The aquaculture veterinary practitioner must realize that there is a significant concerted backlash against salmon farming by several vested interests (both economic and philosophical). He/she must stay apprised of the issues and provide sound, objective scientific perspectives to both clients and the lay public. Furthermore, practitioners must realize that high-value species aquaculture is a relatively new industry, especially to the developed world, and mistakes will be made as the domestication process continues. He/she must remain professional and objective to fish farmers as well, and be especially assertive on matters of environmental sustainability and food wholesomeness.

References

1.  Covington M. 2004. Omega-3 Fatty Acids. Am Fam Physician 70:133-40

2.  Easton MDL, D Luszniak, E. Von der Geest. Preliminary examination of contaminant loadings in farmed salmon, wild salmon and commercial salmon feed. Chemosphere 46: 1053-1074

3.  Hites RA, JA Foran, DO Carpenter, MC Hamilton, BA Knuth, SJ Schwager. 2004. Global assessment of organic contaminants in farmed salmon. Science 303: 226229.

4.  Knapp G. 2003. Change, challenges and opportunities for wild fisheries. Presented at: Conference on Marine Aquaculture: effects on the west coast and Alaska fishing industry. Nov. 17-19. 2003. Seattle, WA.

5.  Mitchell H. 2004. Global Aquaculture. Presented at: 35th meeting of the International Association of Aquatic Animal Medicine. Special pre-conference session: Expanding private practitioner opportunities in fish medicine. April 4. Galveston, TX.

6.  Schiedt K, FJ Leuenberger, M Vecchi, E Glinz. 1985. Absorption, retention and metabolic transformations of carotenoids in rainbow trout, salmon and chicken. Pure & Appl. Chem. 57(685-692).

7.  Torrissen OJ. 1986. Pigmentation of salmonids--a comparison of astaxanthin and canthaxanthin as pigment sources for rainbow trout. Aquaculture 53 (271-278).