Approximately how much of their metabolic energy do fish spend maintaining osmotic homeostasis?

1. Many marine invertebrates have internal salt levels matched to their environments, making them isotonic with the water around them. 2. Fish are not matched to their surroundings and must actively defend their internal balance. 3. They spend approximately five percent of their metabolic energy maintaining osmotic homeostasis. 4. That figure is small enough to be sustainable, so the much larger shares in the last two options would leave little energy for anything else. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 5 "Structure and Function of Plasma Membranes", section 5.2 Passive Transport_