Interesting. There could be something to it. Of course that would make it difficult to explain why some of the highest hatchery smolt to adult return rates occurred during the period when hatcheries were plumbed with ductile iron prior to newer plumbing with PVC and lower survival rates. Anyone looking for the hatchery bogeyman needs to examine all probable factors affecting survival relative to one another. I don't expect iron piping in hatcheries to rank very high on that list.

Sg

What you say makes sense.... But a case in point that comes to mind was the Lewis river...

The hatchery program there consistly produced fish but once the fish first program was started, utilizing the net pens the return rates were significantly higher. I always chalked it up to a few things.

1. The area they were released from at the net pens seemed to keep the returning fish mid river and more exposed to anglers.
2. They were more aggressive biting fish. Perhaps their environment they were raised factored in.

But it's interesting that the net pens from my memory didn't have much if any iron in them, it was mainly PVC...

Keith