esshup says "Trout aren't happy with less than 7 mg/l DO. 5mg/l is pushing their limit."
This information is true for normal water temperatures of 50-65F that are preferred by trout. However I am not sure that 5ppm is the lower DO limit for trout when water temperature is 39F or lower. My EPA water quality criteria book says for DO: 1. "fish vary in their oxygen requirements according to species, age, activity, temperature, and nutritional state. 2. fish are found from time to time and can survive for awhile at oxygen concentrations considerably below that considered suitable for a thriving population;" They (EPA manual) goes on to say that "few investigators have employed methods or sought endpoints that can be related with confidence to maintaining a good fish population."
Trout are not perch or other similar type of fish species but my DO testing shows that YP and some other fish species at 35F-39F will tolerate dissolved oxygen down to 1ppm and even less when normally 3ppm is said to be their lower limit for DO. I think a similar fish physiology response would apply to trout. As their body temperature decreases below their preferred temperature,,, their body physiology also decreases, and their cellular demand for oxygen also decreases. Although the lower DO limit for trout in 39F water would MAYBE be closer to 3 or 4ppm rather than 5ppm. We might be surprised that rainbow trout can even tolerate 2 - 2.5 ppm DO in water 37-39F (3-4C).
I would very much like to find research or any private testing that shows the lower DO limit for trout in water temps less than 39F (4C). I have worked very little with trout in ice covered ponds thus my testing of this feature is very limited. We have to remember that under ice cover when the pond is in the later stages of DO consumption the DO is continually decreasing and DO usually does not stabilize at 3, 2, or 1ppm. Thus the time frame is usually relatively short for low DO that would sustain trout or any fish.
Last edited by Bill Cody; 01/14/22 12:02 PM.
