In these organs in most fish, water flows the opposite direction to the blood, increasing oxygen transfer
[DOC] [TLE] Gas Exchange in Fish | S-cool, the revision website [PAR] Nov 13, 2015 ... After this the blood can pick up no more oxygen from the water ... Countercurrent 
flow As the blood flows in the opposite direction to the water,... [DOC] [TLE] Breathing [PAR] Transfer of oxygen from the water to the tissues involves four steps: gill ventilation
,; branchial diffusion,; blood-oxygen transport,; tissue diffusion.