How doe fish exchange sodium and potassium

[arauca]

We have salt water fish and fresh water
do both fish ( salt & fresh ) contain same amount of potassium in the cytoplasm ?
If the salt water have sodium in the cytoplasm would it be more swollen ?

 

[Moontanman]

We have salt water fish and fresh water
do both fish ( salt & fresh ) contain same amount of potassium in the cytoplasm ?
If the salt water have sodium in the cytoplasm would it be more swollen ?

Fish use their kidneys to maintain a balance of salts inside their bodies and cells. Saltwater fish excrete salts in the form of very concentrated urine.

Freshwater fish excrete very dilute urine that is mostly water to keep the salts from being leached from their bodies.

Sharks go a different route and maintain urea in their bodes in a highly concentrated form to keep the salts in sea water from leaching the salts from their bodies.