What process do bony fish primarily employ concerning water balance?

Bony fish primarily employ the process of excreting water and taking in ions to maintain water balance, especially when they are in a saltwater environment. These fish are hyperosmotic to their surroundings, which means they have a lower salt concentration in their bodies compared to the saline water. To counteract the osmotic pressure that pulls water out of their bodies, bony fish actively excrete urine that is more dilute than their body fluids, allowing them to lose excess water.

Simultaneously, they take in ions, particularly sodium and chloride, through their gills and through their diet to maintain their internal salt levels. This ion uptake is crucial for maintaining osmotic balance and enabling physiological processes to function properly. Thus, by excreting large amounts of water while absorbing necessary ions, bony fish effectively manage their water balance in a challenging marine environment.