1. Troutnut Forum
›
2. Fly Fishing
›
3. Gulping for air

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?


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?

I saw a guide in Quebec highly recommend stroking your hand on an Atlantic Salmons stomach back towards the head to remove air from the body cavity before release while holding the fish in the water. I'd never seen, or heard of that before.

The countercurrent exchange system is a way that the fish's circulatory system takes advantage of the physics of diffusion to get the most oxygen out of the water (and to get rid of the most carbon dioxide). The most oxygen-starved blood is exposed to the least oxygenated water and the most oxygen-rich blood is exposed to the most oxygenated water (this is a progressive process). Either way, oxygen will enter the bloodstream via passive diffusion, because there will be relatively more oxygen (or less carbon dioxide) outside the fish's bloodstream at that point. Sometimes this correlates with flow of water around the main body of the fish; other times, it may not. It depends on the natural direction of flow of the water over the particular structure that contains the capillary that contains the blood. Fish are pretty good at moving the water by themselves to generate the necessary water flow. I don't know that pushing or pulling the fish will make much difference, but I could be wrong. I'd actually be concerned about introducing more stress. Maybe someone can show me where I might be wrong. If you find an error in my explanation, don't hesitate to point it out either. It's been a long day and a few weeks since we covered this in class...

So in the case of the gill structure and the direction of the blood flow through the capillary system this "natural direction of flow" of the water would be thru the mouth and out thru the gills. Should the water flow direction be hindered or reversed I would think that the gas diffusion process would be less efficient. That is point I'm trying to get at.

In streams I hold them facing upstream in the current until they can swim on their own. In standing waters I just hold them gently and let their gill pumping do the work.

Jonathon

It's my understanding that pulling the fish back and forth is counterproductive, as Konchu and Falsify suggest, and that Jonathan's approach is better. I've never heard of the method Sayfu describes that guide using. Jason?

Perhaps moving the fish around would stimulate it to start moving water past its gills, if it had stopped doing so due to stress or shock.

I think in general if a fish isn't even trying to pump its gills, it's gone to meet it's maker, so to speak. No matter how exhausted any fish I've ever caught is, it still seems to be able to work its gills. Just gotta get the head back in the water ASAP!

Jonathon