Abstract
Calcium content of water is of fundamental importance for freshwater snails since it is correlated with growth rates, egg fertility and fecundity. In this study, calcium uptake from the external medium (tap water) in two groups of freshwater snail Planorbarius corneus L. was compared: 200 control snails permanently maintained in tap water, and 200 experimental snails exposed to solutions with high calcium concentrations (214–2137 mg/L) for six weeks before the measurements. The results showed higher uptake in control snails (0.8 mg Ca2+ per snail/day) than in experimental snails (0.4 mg Ca2+ per snail per day), P<0.001. Measurements of Ca2+ in shells and tissues showed a higher calcium content in experimental snails than in control snails, both in the shells (P<0.02) and in the tissue (P<0.05). Lower shell/tissue calcium ratio and lower organic mass loss by ashing showed that experimental snails stored 1.5 times more Ca2+ in soft tissues compared with control snails. Empty dry shells of the control snails accounted for 27% of the total body mass, and in the experimental snails, shell mass was 34% of the body mass. The results suggest that the lower uptake by experimental snails was caused by previously accumulated high quantities of calcium in shells and soft tissues. These findings enhance our understanding of calcium homeostasis in freshwater gastropods and indicate their adaptability to environments with fluctuating calcium levels.