An adult human at rest breathes about 500mL air per breath, at about 12 breaths per minute. The inhaled air is about 21% O2, and the exhaled air is about 16% O2.
The density of air is 1.225 kg/m3, which is 1.225 g/liter. So 5% of a half-liter breath is, ballpark, 0.03 grams oxygen per breath, which at one breath per five seconds is 0.006 grams oxygen per second.
Dissolved oxygen in ocean water is about 0.008 g/liter. Fish are very efficient at extracting this, up to 80%. Squids and octopi are much less efficient, with octopi hanging out more in the 40% range, and squids much lower.
So this means that for every liter of water processed, an example octopus receives 0.003 grams oxygen, and if such an octopus were able to process two liters of water per second across their gills, they would receive as much O2 as a human.
This is not such an incredibly high number that it rules out cephalopod intelligence, especially when considering size differences.
An adult human at rest breathes about 500mL air per breath, at about 12 breaths per minute. The inhaled air is about 21% O2, and the exhaled air is about 16% O2.
The density of air is 1.225 kg/m3, which is 1.225 g/liter. So 5% of a half-liter breath is, ballpark, 0.03 grams oxygen per breath, which at one breath per five seconds is 0.006 grams oxygen per second.
Dissolved oxygen in ocean water is about 0.008 g/liter. Fish are very efficient at extracting this, up to 80%. Squids and octopi are much less efficient, with octopi hanging out more in the 40% range, and squids much lower.
So this means that for every liter of water processed, an example octopus receives 0.003 grams oxygen, and if such an octopus were able to process two liters of water per second across their gills, they would receive as much O2 as a human.
This is not such an incredibly high number that it rules out cephalopod intelligence, especially when considering size differences.