Paralytic shellfish toxins in zooplankton, mussels, lobsters and caged Atlantic salmon, Salmo salar, during a bloom of Alexandrium fundyense off Grand Manan Island, in the Bay of Fundy

Abstract

Substantial mortalities of Atlantic salmon ( Salmo salar) at two aquaculture sites in Long Island Sound, off Grand Manan Island, Bay of Fundy (BoF) (New Brunswick, Canada) in September 2003, were associated with a bloom of Alexandrium fundyense (>3 × 10 5 cells L −1), a dinoflagellate alga that produces toxins which cause paralytic shellfish poisoning (PSP). Cells of A. fundyense collected from surface waters while fish were dying had total paralytic shellfish (PS) toxin concentrations of 70.6 pg STX equiv. (saxitoxin equivalents) cell −1 and PS toxin profiles rich in carbamate toxins (78.2%). The zooplankton sampled contained PS toxins (63.1 pg STX equiv. g −1 wet wt) and the toxin profile matched that of A. fundyense cells. Mean PS toxin levels were low (<4 μg STX equiv. 100 g −1 wet wt) in stomach, gill and muscle tissues of moribund salmon, suggesting that PS toxins are very lethal to salmon. The PS toxin concentrations in blue mussels ( Mytilus edulis) growing on the salmon cages (37; 526 μg STX equiv. 100 g −1 wet wt) were the highest recorded to date from this region. Their PS toxin profiles showed enhanced carbamate contents (85.5%) compared with that found in A. fundyense. Blue mussels collected from an adjacent Canadian Food Inspection Agency (CFIA) monitoring site in Grand Manan had PS toxin concentrations of 4214 and 150 μg STX equiv. 100 g −1 wet wt in late September and December, respectively, well above the regulatory limit (RL), and horse mussels ( Modiolus modiolus) collected in late September had PS toxin concentrations of 2357 μg STX equiv. 100 g −1 wet wt. Detoxification under laboratory conditions suggested that blue mussels may require up to 19 weeks for elimination below RL when they accumulate these high concentrations of PS toxins. This depuration period may be shorter in the field. PS toxin levels above RL were detected in hepatopancreatic tissues of lobster ( Homarus americanus), with lower levels (<16 μg STX equiv. 100 g −1 wet wt) in tail muscle and gills. These results illustrate the movement of PS toxins through the marine food chain following an A. fundyense bloom in the BoF, and support earlier studies suggesting that kills from the region of zooplanktivorous fish, such as herring ( Clupea harengus harengus), can be attributed to blooms of A. fundyense. This is the first reported incident of PSP associated with mortalities of caged Atlantic salmon in the BoF. Analyses of muscle tissues and viscera from the affected salmon indicated that any portion would not be a health hazard if consumed.