What is a key characteristic of bony fish in terms of water and ion management?

Bony fish, particularly those living in marine environments, have adapted specialized mechanisms for water and ion management due to the challenges presented by their saline habitat. One key characteristic of these fish is that they must expel excess salt while conserving water. In this context, they actively expel water through their gills, which is essential for maintaining osmotic balance in a hypertonic (saltier) environment.

To manage ions, marine bony fish utilize specialized cells in their gills called chloride cells that help excrete excess sodium and chloride ions. This process allows them to take in essential ions from the seawater while simultaneously producing concentrated urine to minimize water loss. This combination of expelling water, taking in ions, and producing concentrated urine is vital for survival in salty waters, helping maintain homeostasis despite the dehydrating effects of the environment.

In contrast, fish that live in freshwater environments typically absorb water from their environment and produce large amounts of dilute urine to rid themselves of excess water. Therefore, recognizing the unique adaptations of bony fish in marine settings helps clarify the specific mechanisms and challenges they face regarding water and ion management.