am Hopkins wrote:

Chlorine in water reacts with living tissues and organic matter causing cell
death (acute necrosis) in fish. Since fish gills are sensitive and exposed
directly to the aquatic environment, the death of cells in the gills - the
fish's breathing apparatus - can lead to respiratory difficulty and
asphyxiation.

Thanks all for your replies. I'm now even more motivated to rid my tap water of chlorine down to
0.00000001 ppm. (grin!)

- David