A mammal would have to breathe 800 times more volume to throughput the same weight of medium, so, in a given time, the fish puts through more oxygen than the land animal.
Considering salmon and tuna and sea iguanas and turtles, reptiles aren't more active than fish, and air is inefficient to lift against, so sharks and mammals move at around the same speed. Great white sharks and humans have the same hemoglobin concentrations, 14g/l.
We can also compare a great white shark and a killer whale, a tuna and a wolf.
Yes the maximum available oxygen is higher on land, although the limiting factor for energy throughput can be measured through food consumption and metabolism temperature:
Dolphins consume 4-10% of their bodyweight per dayTuna consume 5-15% of their bodyweight per day.