Final answer:
Marine invertebrates are typically isosmotic with their environment, while fish are hyperosmotic to their marine environment, resulting in different osmoregulatory strategies.
Step-by-step explanation:
Most fish are hyperosmotic to a marine environment, while most invertebrates are isosmotic to a marine environment.
Marine invertebrates generally have internal salt levels that are matched to the seawater, making them isosmotic and thus osmoconformers. They regulate their internal salt concentrations to be consistent with that of the seawater. Conversely, fish, particularly saltwater fish, are hyperosmotic compared to the seawater and must actively excrete salt through their gills and produce concentrated urine to maintain osmotic balance. The effort to maintain osmotic homeostasis requires about five percent of their metabolic energy. Freshwater fish, on the other hand, live in a hypotonic environment compared to their cells and must actively take in salt through their gills while excreting dilute urine to rid themselves of excess water.