FLYMPH FORUM

Mike

Another superb article. I know it will take me awhile to digest what I have read. Considering the content of the article, this will be a simple and embarrassing question. In the hot summer months when the oxygen content is rather low, do not the fish go below the thermocline to both escape the heat as well as increase the oxygen content?

Mike,
One of the articles linked states that larger fish are more affected by lower levels of dissolved oxygen. Is this a result of greater metabolic needs? Also, would it be safe to assume, because of this, that in a tailwater which consistently releases water from a high elevation on the dam that the concentration of larger fish would increase as one gets closer to the dam? If there is more DO present in this water, is there a level above which there is no benefit to fish or other organisms? The same article states that a concentration of 5mg/L is ideal, but the article seemed to be related mostly to ponds. I wonder how much of this applies to trout and if they have greater DO requirements than stillwater species.

I know that's a lot of questions but it is a fascinating topic, and I am interested in anyone's thoughts on these conclusions.

Hi Mike;

I used to perform weekly stream monitoring at work, taking samples and recording DO & temperature before and after our project. Although this is a warmwater stream I observed the following: any rapid change in any parameter be it temperature, dissolved oxygen.pH, conductivity would cause animals in the stream to show signs of stress. This included going to the surface for oxygen, trying to get out of the stream(there used to be a lot of problems with wastewater treatment plant discharges from our neihbor) or finally massive fish and other critter kills. I also noted the following for dissolved oxygen and fish activity: DO >7ppm <10ppm if temperatures were high enough for fish to be active all were happy. DO <7ppm but > 5ppm, largemouth bass became stressed and inactive but bluegill seemed ok. DO <5ppm but >3ppm, bass gone or dead bluegill stressed inactive or starting to die. DO <3ppm, carp start gulping air from surface, catfish and eels start swimming around kinda looked like they were trying to find greener pastures as it were. At same time bugs, tadpoles, and frogs were at the surface.

Someday when I do some trout fishing I'll have to bring as DO meter with me just for kicks.

Wayne