Uptake and transfer of microcystins in noble crayfish in Lake Steinsfjorden, a cyanobacterial (Planktothrix) dominated lake

The Norwegian Lake Steinsfjorden, a major fishery-lake for noble crayfish, is often affected by cyanobacterial blooms caused by microcystin (MC) producing Planktothrix. A recent study demonstrated the presence of microcystins in noble crayfish originating from this lake. However, little is known about the impact of toxic cyanobacteria on crayfish health and crayfish as food-source. We have investigated the presence of MC in noble crayfish from Lake Steinsfjorden, and elucidated whether MCs are transferred and accumulated in vital organs and the edible parts. In 2015, crayfish were captured each month from June to October. Water samples were taken simultaneously. Tissue samples from tail muscle, intestine, stomach, and hepatopancreas were harvested for MC-analysis using an in-house method for enzyme-linked immunosorbent assay (ELISA). MC-analysis results for tissues and water samples were compared. Stomach, intestine and hepatopancreas contained the highest concentrations of MCs, respectively, suggesting that the crayfish acquire large amounts of MCs through diet, which is transferred to the hepatopancreas. The tail muscle contained very low MC-concentrations, with a tendency to decline towards the autumn where the measured MCconcentrations in the water dropped substantially. Results indicate that a normal portion of boiled crayfish tails (~100 g muscle) from Lake Steinsfjorden in 2015 was well below the tolerable daily intake (TDI) limit for MCs (0.04 μg/kg body weight) for adults. However, removal of the intestine from the tails seems a reasonable food safety precautionary measure for consumption of crayfish from cyanobacterial-dominated waterbodies, since the intestine would more than triple the MC-content if not removed.