Final answer:
Euryhaline fish have the ability to live in both freshwater and saltwater by employing osmoregulatory mechanisms to manage their internal salt and water balance. They actively control salt intake and urine concentration depending on the environment, which is essential to their survival.
Step-by-step explanation:
Fish that can survive in both freshwater and saltwater environments are known as euryhaline species. They possess specialized osmoregulatory mechanisms allowing them to maintain water and electrolyte balance despite varying concentrations of salts in their external environments. In freshwater, which is hypotonic to their cells, these fish absorb salt through their gills and excrete diluted urine. Conversely, in saltwater, which is hypertonic relative to their cells, they excrete salt through their gills and produce highly concentrated urine. This balance of salt and water is essential for their survival and requires a significant part of their metabolic energy.
Additionally, the nutritional content of bony fish varies widely; some are lean, while others are more fatty, depending on their diet and environment. Diets can range from algae and smaller fish to detritus and dead organisms. Bony fishes, including ray-finned species like tuna and salmon, demonstrate a diverse array of survival strategies in various aquatic situations.