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Lethal DO levels but fish survive & thrive. HOW?
#521562 05/25/20 07:40 AM
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So after a few years of battling, I have now had three years of winter survival from my trout. The problem is I do not understand HOW they are surviving. Not only are they surviving, they are thriving. On 10.05.2018 I stocked 100 Splake that were 5"-8". Iced over completely by 11.05.2018 and didn't fully come off until 06.15.2019. We caught our first Splake on 06.23.2019 and he was 14"-15". Not only did these fish survive under the ice at supposedly extremely lethal DO levels, they doubled in size! For those of you that aren't familiar with my battle, I have never been able to keep a hole open in my ice throughout winter. I'm at 10,000' elevation so a tough environment. I now KNOW the ice is doming up over my diffusers and making it impossible for the aeration to chew through the ice because the water from the plume is no longer contacting the ice. It took a trip up to the cabin this past Christmas for me to discover this doming issue was the problem.

The last two years we have measured a low DO of .8PPM. Measurements have been taken in different spots over the last two years and found the same number. In December 2019 I measured 1.5PPM maybe 30 yards away from diffuser plume. In February 2020 my buddy measured .8PPM. DO below 5.0PPM is stressful for trout. Lethal DO levels for trout is supposedly somewhere between 2.0PPM to 3.0PPM. He also measured .8PPM in Winter 2018/2019. So I am totally confused how my fish are surviving such low DO conditions for an extended period of time. My water temps during these times are 32.5F to 33F.

So, basically everyone on this forum is smarter than me so I'd love to hear some input!

THEORIES:

1. My meter is inaccurate and showing lower than actual.
I am using a YSI Pro ODO DO meter to take measurements. Supposedly as good as they come. A couple things make me doubt meter inaccuracy. We have recorded .8PPM in different years as the low of the year. On 05.23.2020 my buddy recorded DO of 9.2PPM. If the meter was low by 2 PPM or so that would mean my DO currently is over 11PPM. I do not even think 11PPM is possible at 10,000' elevation.

2. Trout are surviving in the diffuser plume.
It has been posted that in near freezing water a diffuser can affect water 200' away. There is some stuff on Youtube (from a guy in MN) that shows under ice water movement from a single diffuser even farther away than that. This year I measured 1.5PPM 60' or so away from a quad plume and got 1.5PPM. Seems unlikely to me that 30' closer to the plume would have led to DO over 3.0PPM. Also seems unlikely to me that the trout would double in size when confined to living in a 30' circle over the plume.

3.I am venting the poisonous gases and that's what would really kill the trout.
I don't have a hole open, but I do think SOME air from the aeration is venting out of the lake somewhere - just not making a hole. I think it is probably leaking out between the ice and the shore somewhere near each diffuser. So maybe while my water is not contacting atmosphere and exchanging O2, it IS still able to vent the poisonous gases like Hydrogen Sulfide?? Maybe in low DO winterkills it isn't really the low DO that kills the fish. Maybe it is the concentrated gases that deal the death blow???

4. At water temps of 32.5F trout are indestructible
You just can't kill them because they aren't even really breathing anyway!

5.God eventually smiles on the dog (me) that hangs on long enough.
I think that one is self explanatory.

Last edited by wbuffetjr; 05/25/20 07:49 AM.

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Re: Lethal DO levels but fish survive & thrive. HOW?
wbuffetjr #521566 05/25/20 07:58 AM
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2. Trout are surviving in the diffuser plume.
It has been posted that in near freezing water a diffuser can affect water 200' away. There is some stuff on Youtube that shows under ice water movement from a single diffuser even farther away than that. This year I measured 1.5PPM 60' or so away from a quad plume and got 1.5PPM. Seems unlikely to me that 30' closer to the plume would have led to DO over 3.0PPM. Also seems unlikely to me that the trout would double in size when confined to living in a 30' circle over the plume.

It seems to me that oxygen exchange from aeration must occur at the top of plume. The surface tension of the bubbles is so high ... probably little exchange occurs there while air is rising. However, at the top of the plume, there would be an air space hollowed under the ice and a lot of turbulence breaking surface tension that would allow for oxygen exchange. The coldest water is near the surface so the oxygenated water would be chilled near the surface. How deep did you take the measurement when 60' away? If it was not in the top 3 or 4 feet, then indications may be deceiving.

At this point you have evidence that O2 is higher 60' from the plume than it is further away from the plume. As to doubling in size ... whatever water is a refuge to trout is also a refuge for their food. If sufficiently concentrated I could see such fantastic growth resulting. The prey items would find the refuge in the same way that trout do ... they would follow the O2 gradient in the direction of increasing O2.

Re: Lethal DO levels but fish survive & thrive. HOW?
jpsdad #521567 05/25/20 08:05 AM
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Some Clarification

We did not measure .8PPM and 1.5PPM at the same time. The water seems to stay fully mixed under the ice. When I measured 1.5PPM in December it was top to bottom in ~15' of water. When my buddy measured .8PPM in February it was top to bottom in ~10' of water iirc.

I don't see how there could be O2 exchange going on in the dome under the ice. Wouldn't any O2 trapped under the dome get exchanged out and used up fairly quick??

The prey items in the lake like fatheads survived in there at least a decade before I installed aeration. The scuds have probably been in there for eons. So I definitely don't think the prey is living in the plumes.


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Re: Lethal DO levels but fish survive & thrive. HOW?
jpsdad #521570 05/25/20 08:21 AM
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Originally Posted by jpsdad
... whatever water is a refuge to trout is also a refuge for their food. If sufficiently concentrated I could see such fantastic growth resulting. The prey items would find the refuge in the same way that trout do ... they would follow the O2 gradient in the direction of increasing O2.
This sort of reasoning is genius. It happens in the sky, in the water and on land. If environmental pressure moves prey and predator closer together, its a free for all.
I'm not an expert on oxygenation, but I think jpsdad is spot-on here.


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Re: Lethal DO levels but fish survive & thrive. HOW?
wbuffetjr #521571 05/25/20 08:29 AM
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I don't see how there could be O2 exchange going on in the dome under the ice. Wouldn't any O2 trapped under the dome get exchanged out and used up fairly quick??

I don't understand what you are asking. The exchange of oxygen into the water can only happen in one direction. It can only increase the DO. Organisms using the O2 will lower the DO. But if both are happening, isn't this the answer you are looking for? Could it not be said that O2 dissolving in the water is supporting metabolism? Its obvious that the trout's metabolism wasn't shut down. They doubled in size.

Here's how I look at. The trout could not double in size unless food was available to them. This means that where ever the fish are, so is sufficient oxygen to support them and their food and enough to also support the trout metabolism requirements to double in size. I would suggest this. Next winter, go out with a fishing pole, auger, and a sonar and leave the DO meter at home. Where you find the fish ... there lies the answer to what is supporting them. They will only be in water that provides everything they need.

Just a quick question. Do your trout double in size during the growth season in summer? If not, you have strong evidence that the prey of the pond is concentrated in a smaller volume of water during winter.

Last edited by jpsdad; 05/25/20 08:56 AM.
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Re: Lethal DO levels but fish survive & thrive. HOW?
jpsdad #521585 05/25/20 12:23 PM
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Jpsdad - The ice dome is a closed system. As the dome increases in size (the ice lifts farther and farther off the water) it actually increases the PSI on my pump. The air from the plume does not contact the outside atmosphere - it only contacts the air trapped under the dome. What I am asking is this, wouldn't the air trapped under the dome run out of O2 to exchange?

The trout grow even more in the summer than the winter. When we have stocked fish in late June or early July they have usually doubled or almost doubled by late September.

I don't necessarily think the fatheads or scuds NEED a refuge. They survived every year before there was ever any aeration.

Last edited by wbuffetjr; 05/25/20 12:24 PM.

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Re: Lethal DO levels but fish survive & thrive. HOW?
wbuffetjr #521586 05/25/20 12:53 PM
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I was curious about how much (if any) gas exchange happens THROUGH the ice. I had always been assuming none. Found this old paper (https://www.tandfonline.com/doi/abs/10.3402/tellusa.v11i3.9311), which confirms no exchange occurs. Gases do get released when ice melts, so oxygen trapped in the ice will be released into the dome pocket. It potentially could account for *some* oxygen entering the water column.

If the dome breaking pole system is effective, you may have cracked this nut. 🤞


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Re: Lethal DO levels but fish survive & thrive. HOW?
wbuffetjr #521594 05/25/20 03:54 PM
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Originally Posted by wbuffetjr
Jpsdad - The ice dome is a closed system. As the dome increases in size (the ice lifts farther and farther off the water) it actually increases the PSI on my pump. The air from the plume does not contact the outside atmosphere - it only contacts the air trapped under the dome. What I am asking is this, wouldn't the air trapped under the dome run out of O2 to exchange?

Thank you for clarifying. I am just sitting thinking ...

It seems to me that if the air pump is able to move air that goes through the diffusers then new air is going into the system all of the time. Now I don't know what cfm your air pump can generate but you are at least putting the air fully charged with oxygen into the pond at that rate. There is ~.08 lbs of O2 in every cubit ft (@ sea level) ... 10,000 feet it would be less. For now lets assume .06 lbs of O2 per cu ft. So at 10 cfm there would be 864 lbs of O2 entering the pond every day via the pump. To be sure, the water doesn't dissolve all of it but as far as a lack of O2 in the dome ... no ... I think the difference in O2 there and the atmosphere is likely small where the difference is caused by oxygen dissolving into the water. There must be cracks or a spill point that lets the air out, If no air leaks out, then every ounce of it is dissolved into the water, and so I think it more plausible that it leaks out of the dome some how. I don't know what cfm is being pumped or what percentage of the oxygen is dissolved but I think it is clear that only a fraction of 10 cfm would need to be dissolved to support the fish. DO will dissolve mostly at the interface of the dome air and water surface.


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The trout grow even more in the summer than the winter. When we have stocked fish in late June or early July they have usually doubled or almost doubled by late September. I don't necessarily think the fatheads or scuds NEED a refuge. They survived every year before there was ever any aeration.

It would be normal for growth to be greatest during the summer.

I wasn't for sure exactly what you meant by doubling. Whether it be weight or length. If length is doubled, the weight is more than octupled. Either way, the growth of your trout in winter seems extraordinary to me and I think an explanation like "The prey is dispersed throughout the lake and the trout are greatly deprived of oxygen" falls short of explaining this extraordinary growth. Like you, I am seeking answers but the ones I postulated are the only ones that I am comfortable with.

Last edited by jpsdad; 05/25/20 09:25 PM.
Re: Lethal DO levels but fish survive & thrive. HOW?
wbuffetjr #521624 05/26/20 07:44 AM
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Jpsdad and Dr Luke - I definitely appreciate the thoughts. Thank you!!

Jpsdad - At 10 PSI my pump makes 12 CFM at sea level - assuming that is 8 CFM at 10,000' (33% de rate). When I say the trout doubled I mean length. I've never weighed a fish up there. They never used to live long enough to justify owning a scale Lol I don't THINK there are any cracks in the domes. I think once the dome gets big enough the air is travelling horizontally under the ice and venting out at shore somewhere. Maybe even burping out in intervals. I was not able to verify that though. I could not see any evidence of activity around the shore anywhere with binoculars. I did not walk around the shore that is close to the diffusers because I was scared of finding thin ice under snow by falling through. That shoreline is against the timber and holds much more snow than anywhere else on the lake.


Dr Luke - I am hoping the pipes put a stop to the ice domes. The cool part is we are going to install the pipes on two lakes lower than mine as well. One at 9,650' and one at 8,900'. One has a windmill aerator and one has a vertex solar rig. Neither has been able to keep a hole open all winter either and I am certain the domes are getting them as well. Both of those, especially the lower one, are much easier to access in winter than mine so I will get a lot of feedback from snowmobilers on if holes stay open or not.

Last edited by wbuffetjr; 05/26/20 07:45 AM.

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Re: Lethal DO levels but fish survive & thrive. HOW?
wbuffetjr #521641 05/26/20 09:30 AM
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The fish (trout and FH) are breathing. The diffused air is under pressure and being infused into the water (somewhere) and the fish find that/those locations. Many studies and info on fish being able to detect O2 levels and move to the preferred locations. The fish are alive - that is proof of O2 availability.
















Re: Lethal DO levels but fish survive & thrive. HOW?
wbuffetjr #521643 05/26/20 09:45 AM
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Originally Posted by wbuffetjr
When I say the trout doubled I mean length ...

To say I am impressed falls way short of this remarkable achievement through winter. Well done! Aeration is delivering more than just winter survival.

Re: Lethal DO levels but fish survive & thrive. HOW?
wbuffetjr #521661 05/26/20 02:45 PM
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Thanks for the input fellas. I am probably looking for more of an answer than I will ever find. I know there is enough O2 there for survival because they are surviving. Just wonder if they can survive on less than we currently think. I just am having a hard time understanding how we are measuring .8PPM in different locations around the lake and yet somewhere there is this refuge with >5.0PPM.

Jpsdad - Trout in our lake have always outperformed any lake around us. The same fish truck would drop fish in the lower lake then drive on up to drop fish in our lake. By September our fish would have substantially outgrown the lower fish, from the same batch, every single year. We just couldn't ever get them through the winters.


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