Combined effects of waterborne copper exposure and salinity on enzymes related to osmoregulation and ammonia excretion by blue crab Callinectes sapidus
Copper is essential, but can be toxic to aquatic organisms when present in high concentrations. In freshwater crustaceans, copper inhibits enzymes related to ionic and osmoregulation and to the ammonia efflux, that leads to Na+ imbalance and inhibition of ammonia excretion. In the animals inhabiting estuarine or seawater, mechanisms of copper toxicity is not clear, but had been described as disruption of ionregulation and metabolism. To clarify the mechanism of copper toxicity in crustaceans inhabiting variable salinity, this work investigated whether copper affects ammonia excretion and enzymes used for ammonia balance and osmoregulation in the blue crab Callintectes sapidus acclimated to salinity 2 and 30 ppt. To achieve this, juveniles of the blue crab were exposed to 63.5 µg/L of copper at both salinities for 96 h. This is an environmentally realistic copper concentration. Results of ammonia efflux, free amino acids and Na+ concentrations in hemolymph, Na+/K+-ATPase, H+-ATPase and, carbonic anhydrase (CA) activities in gills were consistent with the osmoregulatory pattern adopted by the blue crab, which hyperosmoregulates at salinity 2 ppt and osmoconforms at 30 ppt. At 30 ppt copper reduced free amino acid in hemolymph of crabs, suggesting an effect of the metal on osmotic performance. At 2 ppt, copper significantly increased the H+-ATPase activity involved in ammonia excretion. This may be a compensatory response of crabs to maintain low levels of ammonia in their hemolymph; which can be increased by copper exposure. Results presented here are useful for the improvement of the Biotic Ligand Model (BLM) to predict copper toxicity for saltwater environments.
KeywordsBiotic Ligand Model Crustacean Gills Metal Toxicity
Authors wish to thank Dr. Adalto Bianchini from Universidade Federal do Rio Grande – FURG, RS / Brazil and Dr. Chris Wood from University of British Columbia, BC / Canada for scientific assistance. This work was supported by the Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul from Brazil (FAPERGS - Proc. 1700-12-2). E. G. G. is a graduate fellow from the Brazilian CAPES. M. B. J. was a research fellow of the Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul (FAPERGS – Proc. 1635-2551/13-1) during the development of this work. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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