It is generally accepted that in order to help oxygenate a fish’s blood/oxygen content level before release from a stressful encounter that we aid the flow of water over the gills. This is typically performed by gently grasping the fish just ahead of the caudal fin and rhythmically producing a reciprocating motion to the fish as it lies placidly in the water then releasing the grip when the fish begins to struggle. If considering the (counter current system) and the fish’s respiratory rate
(timing) of water from mouth thru gills process could this be counterproductive?
The blood flows through the gill filaments and secondary lamellae in the opposite direction from the water passing the gills. This is a counter current system and is very important for getting all of the available oxygen out of the water and into the blood.
Consider the following scenarios:
(1) Pushing the fish forward when the mouth is closed.
I see no gain.
(2) Pushing the fish forward as the mouth is opening.
I see little gain as the expanded mouth volume is fixed.
(3) Pushing the fish forward as the mouth is closing and the gill plates are opening.
I see a possible gain.
(4) Pulling the fish backward when the mouth is closed.
I see no gain
(5) Pulling the fish backward when the mouth is opening.
I see no gain at best and a possible hindrance.
(6) Pulling the fish backward when the mouth is closing and the gill plates are opening.
I see this as the worst case scenario. Water pressure is increased at the gill plate opening countering the increased pressure provided by the decreasing mouth volume which provides the means of water flowing through the gills and reduces the effectiveness of the “counter current system”.
What am I misunderstanding?