The effect of dissolved carbon dioxide (CO2) on the bone mineral content and on the expression of bone-Gla protein (BGP, Osteocalcin) in the vertebral column of white grouper (Epinephelus aeneus)

Abstract

The aim of this study was to test the effect of long-term dissolved CO2 exposure on white grouper (Epinephelus aeneus). 45 day post hatching (dph) groupers (0.4 ± 0.05 g; 2.1 ± 0.1 cm) were equally distributed to 15 aquaria (17 L) at a density of 40 larvae per aquarium. The fish were grown for 60 days at a salinity of 25 ppt (26.5 οC) while being exposed to three dissolved CO2 concentrations: Control (0.8 ± 0.1 mg L−1; pH 7.9 ± 0.1), Medium (5.5 ± 0.2 mg L−1; pH 7.1 ± 0.1) and High (28.5 ± 1.5 mg L−1; pH 6.2 ± 0.1). Analysis of bone mineral contents showed that at the end of the CO2 exposure period (105 dph), the Ca levels were significantly higher (P < .001) in the skeleton of fish from the high CO2 treatment as compared to the medium and control treatments. However, the P levels were not significantly different between the three treatments (P > .05). The gene expression of bone Gla protein (BGP, Osteocalcin), a marker for skeletal mineralization, was significantly higher in the vertebral column of the fish from the control treatment as compared to the medium (P < .05) and high (P < .01) treatments. The expression of BGP mRNA was positively correlated with the fish growth rate, as the fish from the control treatment presented the highest body weight at the end of the experiment.