The pelagic species, those that live elsewhere in the water column are neutrally buoyant so they don't need to suspend any energy to stay afloat at the level in which they live. Energy conservation also occurs at the molecular level in the structure of the enzymes which are designed to work at lower temperatures where there is less energy available for them to catalyze reactions. The fish that lack red blood cells and those that have fewer that the temperate fish also conserve energy because it takes less energy to pump the blood and because the hemoglobin and red blood cells do not have to be made. Since Notothenioid fish do not have glomeruli in their kidneys, the antifreeze glycoprotein are never expelled into the wastes from the blood so no energy needs to be used to reabsorb these glycoproteins. Your students might be able to come up with more examples as they go through this suite of activities.
Every reaction is regulated by an enzyme which is a specialized protein that acts as a catalyst.
This is thrifty because it decreases the amount of energy that the organism needs and it protects the organism against the excessive heat that would have to be used if enzymes were not present. Each enzyme can be used over and over since it is not changed by the reaction it regulates. Most enzymes work best at the temperature typical for the organism in which it occurs. At higher temperatures there is more molecular motion so the enzyme can collide with the substrate molecules more often and cause more reactions to happen. This causes the rate of chemical reaction to increase.