Thirteen species of adult marine fish were exposed to hypo-osmotic salinities for more than 2 weeks. Twelve species survived at 10‰, six species at 5‰ and three species at 3‰. No abnormal behavior was observed, but the water content of muscle increased in all species. Shallow-water, inshore species generally appeared to be more tolerant to changes in salinity than deep-water, offshore species. Tolerance of hypo-osmotic salinities varied within a single family or genus. For most species tested, the critical tolerance limit is about 5 to 10‰, and above 10‰ all species survived without apparent abnormal behavior. The present results suggest that many marine fish are more euryhaline than expected, and could be selected for farming in estuaries, provided that production is not reduced in fluctuating salinities. Copyright © 1983 Published by Elsevier B.V.