Intestinal response to ocean acidification in the European sea bass (Dicentrarchus labrax)

Highlights

• High CO2 reduced specific growth rate in sea bass juveniles.

• High CO2 increased intestinal bicarbonate secretion in the anterior and mid intestine.

• High CO2 increased intestinal carbonate precipitates 4.4-fold.

• High CO2 increased intestinal expression for atp6v1b (V-ATPase β subunit), slc4a4, slc26a3, and slc26a6.

Abstract

The intestine of marine fishes contributes to the ocean carbon cycle producing carbonate aggregates as part of the osmoregulatory process. Therefore, this study aimed to evaluate physiological adjustments of European sea bass (Dicentrarchus labrax) intestine to a higher pCO2 environment likely in the near future (~1700 μatm). At the whole-body level, hypercapnia for 5 weeks resulted in fish having a significantly diminished specific growth rate, condition factor and hepatosomatic index. An increase in plasma osmolality and HCO3− concentration was detected, paralleled by decreased metabolites concentrations. In the intestine, high seawater pCO2 was without effect on ouabain-sensitive ATPase activities, while Bafilomycin A1-sensitive ATPase activity significantly decreased in the anterior intestine. Anterior and mid intestine were mounted in Ussing chambers in order to measure bioelectrical parameters and bicarbonate secretion by pH-Stat ex-vivo. Hypercapnia induced a 2.3 and 2.8-fold increase in bicarbonate secretion rates in the anterior and mid intestine, respectively. In the intestinal fluid, HCO3− concentration increased 2.2-fold, and carbonate precipitates showed a 4.4-fold increase in response to hypercapnia, paralleled by a >3-fold increase of drinking and a >2-fold increase of intestinal volume at any given time. At the molecular level, hypercapnia elicited higher intestinal mRNA expression levels for atp6v1b (V-ATPase B subunit), slc4a4, slc26a3, and slc26a6, both in the anterior and mid intestine. As a whole, our results show that the intestine of sea bass responds to high seawater pCO2, a response that comes at a cost at the whole-body level with an impact in the fish specific growth rate, condition factor, and hepatosomatic index.

Alves A., Gregório S. F., Ruiz-Jarabo I. & Fuentes J., in press. Intestinal response to ocean acidification in the European sea bass (Dicentrarchus labrax). Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. Article (subscription required).

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