Answer:
Fish utilise a counter-current system in order to maximise the amount of oxygen that can extracted from water. Water has a much lower oxygen content than air and as such fish need a much more efficient system that can extract a much higher proportion of oxygen from the surrounding water.
Explanation:
Counter flow created more movment and chaos, it made the molecules bump into each other more often, which makes it more likely that each individual partivle will go out of the pores. whereas parelel flow the particles move neatly along side one another
