Freshwater Fish Reside in Hypotonic Environments

Multiple Choice

Freshwater fish reside in hypotonic environments. They do not drink water, and they excrete large volumes of hypotonic urine in an effort to osmoregulate. How do they obtain an adequate supply of electrolytes?

A) There is an increase in Na⁺/K⁺- ATPase activity across the basolateral membrane.
B) Gill lamellae take up additional electrolytes from freshwater.
C) The rectal gland is specialized to produce the dilute hypotonic urine) and conserve ions.
D) Chloride cells transport additional electrolytes into the circulation of these organisms.