Oxygen Levels for fish

[Rob Brownfield]

As many of u may have seen, there has been a bit of a discussion regarding Summer Piking....and Stillwater Barbel etc over the past few weeks. What I want to ask and illustrate is how tough fish can be...

I caught a Jack of about 5 pounds last night that fought really well on my Ultralight gear. (I was after Perch) On landing this fish, I immediatly recognised it as a fish I had caught at the tail end of last year. The reason I know this fish is because on the left side it has 2 semi detached gill rakers, and on the right, one. The rakers are hanging outside the gill covers and are very pale pink, suggesting strongly that the damaged gills receive no blood suppy. This fish not only put an apperance in last night, it liked me so much, that I caught it again 30 minutes later.

This fish can not be getting a good supply of oxygen, yet it is actively hunting, fighting hard, and has survived like this for at least 8 months. Maybe, just maybe, we are being a little too protective of our fish when it comes to summer piking/oxygen use debate etc.....what do u guys think?

 

[Ron Clay]

Let's consider oxygen content of water and how it gets there. Gases such as O2 get into and are dissolved into the water by a process known as diffusion. High O2 levels are caused by optimum temperature (8 to 14 deg C) water in a dynamic state ie as it might be below a weir or waterfall and high barometric pressure. The waterfall causes the surface tension of the water to be broken allowing more O2 to diffuse.

Low O2 levels are caused by high or very low temperatures, still conditions encouraging surface film and low barometric pressure. Any temperature over 20 deg C will cause O2 to flash off.

There is also the effect of weed. It gives off O2 in daylight and CO2 in darkness.

Quite a lot of conditions that affect O2 content isn't it?

Summer conditions can often cause water to have it's highest O2 content provided the temperature is not too high

 

[Chris Bishop]

I've caught pike with gills all over the place that are otherwise healthy. That's not to say you shouldn't be careful though - head up hooking of baits is the usual cause of the problem, as the hooks turn through 180 degrees when you hit a take and can catch the gill rakers.