I think that Ron's remarks hold true for invertebrates. However, they are not true for teleost marine fish. Ron and I discussed this over drinks about 5 years ago at a convention in Vancouver Canada. I am surprised if he would still hold to that view for fish.
Here are some references, but there are certainly more.
Marine teleost fish are more euryhaline than previously believed (Wu & Woo, 1983).
Studies indicate that many reef fish which have been classified as stenohaline exhibit considerable powers of euryhalinity (Wu & Woo, 1983. Woo & Chung, 1995). Physiological assessment indicates that a species may be physiologically euryhaline while ecologically stenohaline. This suggests that the assignment of a species as euryhaline or stenohaline should be dissociated from a consideration of the ecological habitat of the species (Woo & Chung, 1995).
Ancient seawater concentration was believed to be much lower (404mm) than that found today (1123mm) (Spaargaren, 1979). It is likely that future coral reef inhabitants evolved in an environment that was much less saline than present day seas (Moyle, & Cech, 1982). This may account for the ability of marine teleost fish to readily adapt to hyposaline conditions. Cheung, et. al., 1979 determined that boney reef fish can be kept at a salinity (not SG
) of 16ppt "indefinately."
A report in Drum and Croaker stated: “We now have experience that proves that a wide variety of teleosts can live quite comfortably at ½ salinity (1.010) for extended periods of up to 2 to 3 months (Goodlett & Ichinotsubo, 1997). Emperor angelfish Pomacanthus imperator were the subjects of one such study. They were kept in salinities as low as 7ppt for 30 days without any apparent ill effects (Woo & Chung, 1995).