Why do you think keeping salt water shellfish such as clams and mussels in freshwater kills them? support your answer?

I think keeping water shellfish such as clams and mussels in freshwater kills them simply because they absorb water faster than they can eliminate it. Freshwater is hypotononic (more solvent than solute) therefore the hypertonic (more solute than solvent) shellfish takes in more water osmotically, such that there will be no proportionality between absorption and its elimination.