Effects of ammonia stress in the Amazon river shrimp Macrobrachium amazonicum (Decapoda, Palaemonidae)

• Ammonia exposure increases (Na+,K+)-, V(H+)-ATPase and antioxidant enzyme activities.
• Relative expression of V(H+)-ATPase mRNA is increased by ammonia exposure.
• ATPase distribution in gill ionocytes is unaffected by ammonia exposure.
• Total hemolymph hemocyte count is decreased by ammonia exposure.

We evaluate the effects of total ammonia nitrogen-N (TAN) exposure for 72 h on (Na+,K+)- and V(H+)-ATPase activities and on their subunit expressions in gills of the diadromous freshwater shrimp Macrobrachium amazonicum. Specific (Na+,K+)- and V(H+)-ATPase activities increased roughly 1.5- to 2-fold, respectively, after exposure to 2.0 mmol L−1 TAN. Quantitative RT-PCR analyses revealed a 2.5-fold increase in V(H+)-ATPase B subunit mRNA expression while (Na+,K+)-ATPase α-subunit expression was unchanged. Immunohistochemical analyses of the gill lamellae located the (Na+,K+)-ATPase throughout the intralamellar septal cells, independently of TAN concentration, while the V(H+)-ATPase was located in both the apical pillar cell flanges and pillar cell bodies. Systemic stress parameters like total hemocyte count decreased by 30% after exposure to 2.0 mmol L−1 TAN, accompanied by increased activities of the oxidative stress enzymes superoxide dismutase, glutathione reductase and glucose-6-phosphate dehydrogenase in the gills. The stress responses of M. amazonicum to elevated TAN include increases in gill (Na+,K+)- and V(H+)-ATPase activities that are accompanied by changes in oxidative stress enzyme activities, immune system effects and an increase in gill V(H+)-ATPase gene expression. These findings likely underpin physiological effects in a crustacean like M. amazonicum that exploits multiple ecosystems during its life cycle, as well as under culture conditions that may significantly impact shrimp production by the aquaculture industry.