Answer:
Carbon dioxide dissolve readily in sea water hence makes it high in carbonic acid concentration. The fresh water will dilute the concentration of carbonic acid thus preventing the crab from being exposed to high concentrations which can dissolve its shell.
<em>Hope</em><em> this</em><em> helps</em><em> </em><em>!</em>
Based on my research, freshwater fish are a type of fish that has a higher concentration of salt than it's internal environment. With respect to osmoregulation, to fight this circumstance the freshwater fish has a kidney that makes the water to pass quickly.
organ system must be present
