Nontargeted metabolomics reveals biochemical pathways altered in response to captivity and food limitation in the freshwater mussel Amblema plicata.

Effective conservation of freshwater mussels (Mollusca: Bivalvia: Unionidae), one of the most endangered groups of animals in North America, is compromised by limited knowledge of their health. We address this gap in knowledge by characterizing the metabolic profile of Amblema plicata in the wild and in response to captivity and food limitation. Eight mussels brought into captivity from the wild were isolated for 18 days without a food source. Hemolymph samples were taken prior to, and 9 and 18 days after the start of the experiment; these samples were analyzed by gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry. We detected and identified 71 biochemicals in the hemolymph of freshwater mussels; of these, 49 showed significant changes during captivity and/or food limitation (p<0.05). Fasting resulted in severe metabolite depletion. Captive (but fed) mussels experienced changes similar to (albeit less severe than) fasting mussels, suggesting that mussels may experience nutritional deficiency under common captive conditions. A. plicata responded to food limitation stress by preferentially using energy reserves for maintenance rather than growth. Carbohydrate and energy metabolism exhibited down-regulation in captive, food-limited, and wild mussels. Lipid metabolism was up-regulated in captive/food-limited mussels and unchanged in wild mussels. Amino acid metabolism was up-regulated in wild mussels and down-regulated in captive/food-limited mussels. Nucleotide metabolism was up-regulated in the wild mussels, down-regulated in food-limited mussels, and unchanged in captive mussels. The different responses between treatment groups suggest potential for nucleotide metabolism as a biomarker of health status for freshwater mussels.