George and I had some discussion about this mushroom (see its gill side in the next photo). He thinks it might be Lactarius peckii, owing to the radiating circles on the cap and the fact that the latex wasn't particularly sticky. I believe it is in the Lactarius hygrophoroides/volemus, corrugis group because of the voluminous white milk, browning of the gills and distinctly fishy odor. Lactarius peckii also has a shinier cap and darker gills. This specimen has the texture of a L. hygrophoroides or corrugis. I know it isn't L. volemus or hygrophoroides, and it doesn't quiite look like any L. corrugis I've ever seen, so its identity remains a mystery until someone else can guide us in the right direction.