David A. Higgs

Mercury and other trace elements in farmed and wild salmon from british Columbia, Canada

The present study reports measured levels of Hg and other trace elements in commercial salmon feed; farmed Atlantic, coho, and chinook salmon (n 110); and wild coho, chinook, chum, sockeye, and pink salmon (n 91). Metal concentrations in farmed and wild salmon from British Columbia, Canada, were relatively low and below human health consumption guidelines. Methylmercury in all salmon samples (range, 0.03-0.1 g/g wet wt) were below the 0.5 g/g guideline set by Health Canada. Negligible differences in metal concentrations were observed between the various species of farmed and wild salmon. Metal concentrations generally were higher in commercial salmon feed compared to farmed salmon. Mercury showed slight bioaccumulation potential in farmed salmon, with biomagnification factors (BMFs) ranging between 0.8 and 1.9. Other metals, such as Cd, Pb, and Ni, exhibited biodilution, with BMFs of much less than one. The relatively low degree of biomagnification of metals observed in farmed salmon likely resulted from the combination of low gastrointestinal absorption efficiency, negligible transfer to muscle tissue relative to other compartments, and a high degree of growth dilution in these fish. Human dietary exposure calculations indicate intakes of Hg, Cd, Pb, Cu, As, and Ni via farmed and wild British Columbia salmon are a relatively small percentage of total intakes (0.05-32%) compared to other Canadian foodstuffs, such as fruits, vegetables, chicken, and beef (68-99%). Although total dietary exposure of Cd, Pb, and Cu approached provisional tolerable daily intake levels, the contribution from British Columbia salmon was less than 2%. Our findings indicate farmed and wild British Columbia salmon remain a safe source of omega-3 highly unsaturated fatty acid intake for cardioprotective and, possibly, other health benefits.

Postprandial gastrointestinal blood flow, oxygen consumption and heart rate in rainbow trout (Oncorhynchus mykiss).

The present study is the first to simultaneously and continuously measure oxygen consumption (MO(2)) and gastrointestinal blood flow (q(gi)) in fish. In addition, while it is the first to compare the effects of three isoenergetic diets on q(gi) in fish, no significant differences among diets were found for postprandial MO(2), q(gi) or heart rate (f(H)) in rainbow trout, Oncorhynchus mykiss. Postprandial q(gi), f(H) and MO(2) were significantly elevated above baseline levels by 4 h. Postprandial q(gi) peaked at 136% above baseline after 11 h, f(H) peaked at 110% above baseline after 14 h and MO(2) peaked at 96% above baseline after 27 h. Moreover, postprandial MO(2) remained significantly elevated above baseline longer than q(gi) (for 41 h and 30 h, respectively), perhaps because most of the increase in MO(2) associated with feeding is due to protein handling, a process that continues following the absorption of nutrients which is thought to be the primary reason for the elevation of q(gi). In addition to the positive relationships found between postprandial MO(2) and q(gi) and between postprandial MO(2) and f(H), we discovered a novel relationship between postprandial q(gi) and f(H).

Flesh residue concentrations of organochlorine pesticides in farmed and wild salmon from British Columbia, Canada

The present study reports measured levels of organochlorine pesticides (OCPs) in commercial salmon feed (nu2009=u20098) and farmed Atlantic, coho, and chinook salmon (nu2009=u2009110), as well as wild coho, chinook, chum, sockeye, and pink salmon (nu2009=u200991). Flesh residue concentrations (ng/g wet weight) of dichlorodiphenyltrichloroethanes (DDTs), hexachlorocyclohexanes (HCHs), chlordanes, chlorobenzenes (CBz) and cyclodiene pesticides (e.g., dieldrin, mirex) were 2 to 11 times higher (pu2009<u20090.05) in farmed salmon compared with wild salmon. Concentrations were positively correlated with flesh lipid levels. Farmed Atlantic salmon (12-15% lipid) typically exhibited the greatest OCP burdens compared with other salmon species. However, when expressed on a lipid weight basis, concentrations of OCPs (ng/g lipid weight) in wild salmon, in many cases, exceeded those levels in farmed salmon. Observed interspecies and site-specific variations of OCP concentrations in farmed and wild salmon may be attributed to divergent life history, prey/feed characteristics and composition, bioenergetics, or ambient environmental concentrations. Calculated biomagnification factors (BMF =u2009C(F)/C(D), lipid wt) of OCPs in farmed salmon typically ranged between two and five. Biomagnification of chemicals such as DDTs, chlordanes, and mirex was anticipated, because those compounds tend to exhibit high dietary uptake and slow depuration rates in fish because of relatively high octanol-water partition coefficients (K(OW)su2009>u200910⁵). Surprisingly, less hydrophobic pesticides such as hexachlorocyclohexanes and endosulfans (K(OW) su2009<u200910⁵) consistently exhibited a high degree of biomagnification in farmed salmon species (BMFsu2009>u20095). This is contrary to previous laboratory and field observations demonstrating fish BMFs less than 1 for low K(OW) chemicals, because of efficient respiratory elimination of those compounds via gills. The results suggest that ambient seawater concentrations and bioconcentration-driven accumulation may play a key role in the bioaccumulation of these relatively more water-soluble contaminants in farmed salmon. Finally, OCP exposure through consumption of British Columbian salmon is found to be low relative to United States national average per capita total exposure levels and provisional tolerable daily intakes.