What is one way a saltwater fish controls the concentration of salt in its body?

One way a saltwater fish controls the concentration of salt in its body is by drinking large amounts of seawater. This may seem counterintuitive, as seawater is much saltier than the fish's internal environment. However, the fish has special adaptations to deal with this:

* Specialized Gills: Saltwater fish have gills that can actively excrete excess salt from their bodies. They do this by pumping sodium and chloride ions (the main components of salt) out against the concentration gradient, requiring energy.

* Kidney Filtration: Their kidneys also play a role by producing very concentrated urine, further eliminating excess salt. This urine is much saltier than their blood.

These mechanisms work together to maintain a balance, allowing the fish to live in a salty environment despite having a much lower salt concentration in their bodies.