Increased plasma cortisol level as acute response to glochidia parasitism

Acute stress response in the European bitterling, Rhodeus amarus , to glochidia parasitism by the invasive unionid mussel, Sinanodonta woodiana , was quantified by analysing cortisol plasma levels using liquid chromatography coupled to mass spectrometer. We tested a novel method which required as little as 4 µL of plasma by increasing the volume using charcoal-treated plasma. Bitterling were observed to increase cortisol levels significantly in response to glochidia infestation. Overall, this technique allows the precise measurement of steroid hormone plasma concentrations in small fish.