Hey Cecil,
Reading back thru this thread it looks like you were facing a difficult problem. What was the outcome?
Bill D.
I cranked up the well and morbidity and mortality stopped. It was not due to temp, ammonia, nitrites, or nitrates AFAIK as I have monitored those parameters in susequent autumns, and they were not an issue with the well shut off. It could be an issue of fighting as low levels of iron, when the well is cranked up may reduce that by reducing visibility. Or for some reason the parasites are more of an issue if the pond is not flushing?
IIRR I later used PP on the pond at a minimal level of 2 mg/l and the trout did not like it -- even with a Kasco surface aerator running full bore. Many came to the surface severely stressed and were netted out and whole frozen and sold to taxidermists. So not a huge loss. Interestingly there were about 25 healthy trout in the pond come spring so I may have jumped the gun. Perhaps I should have waited a lttle longer, but on the other hand if they had gone to the bottom and died that would have been a bigger loss.
Did read later that PP is a big no no in high pH waters. That said I've treated tilapia in an indoor tank with no problems.
I have since raised another crop of brook trout with 6 of them over 6 lbs., and once again experienced low mortality rates and morbity. But no external marks like those in the picture. However a very small percentage of the population. Not an issue with the other species of trout whatsoever.
It could also be an issue of the shorter lifespan of brook trout, or may have been related to the feed, as even feeding only once a day the fish were real tubbies.
(The bottom two are females full of eggs)