Exposure to domoic acid causes oxidative stress in bay scallops Argopecten irradians

Abstract

The neurotoxin domoic acid (DA) is produced by Pseudo-nitzschia spp. during harmful algal blooms and is linked to amnesic shellfish poisoning. This toxin is particularly problematic in the culture of bivalves for human consumption. In this study, we exposed bay scallops to 20, 40, and 60 ng/ml DA and examined toxin accumulation and stress response at 3, 6, 12, 24, 36, and 48 h of exposure. Oxidative stress was determined by measuring the levels of superoxide dismutase (SOD), catalase (CAT), heat shock protein 90 (HSP90), and metallothionein (MT) in the digestive diverticula and/or hemolymph and by determining H2O2 concentration in hemolymph. We also observed histological changes to gills following exposure to DA in order to determine changes in melanization. We found that scallops accumulated a maximum of 2.61 ng/ml DA in their digestive diverticula when exposed to 60 ng/ml. Stress indices rose under higher DA concentrations, and HSP levels increased under exposure to higher concentrations of DA. However, mRNA expression and activity of other stress parameters showed peaks at different times during exposure, with subsequent declines. Epithelial melanization of gills indicated a strong positive response to DA at 60 ng/ml for 48 h (P < 0.05). These results indicate that exposure to DA induces oxidative stress, disrupts metabolism, and has negative effects on the defense systems of bay scallops.