No evidence for a critical salinity threshold for growth and reproduction in the freshwater snail Physa acuta

Elsevier Sci Ltd
Publication Type:
Journal Article
Environmental Pollution, 2005, 134 (3), pp. 377 - 383
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The growth and reproduction of the freshwater snail Physa acuta (Gastropoda: Physidae) were measured at various salinity levels (growth: distilled water, 50, 100, 500, 1000 and 5000 muS/cm; reproduction: deionized water, 100, 500, 1000 and 3000 muS/cm) established using the artificial sea salt, Ocean Nature. This was done to examine the assumption that there is no direct effect of salinity on freshwater animals until a threshold, beyond which sub-lethal effects, such as reduction in growth and reproduction, will occur. Growth of P. acuta was maximal in terms of live and dry mass at salinity levels 500-1000 muS/cm. The number of eggs produced per snail per day was maximal between 100 and 1000 muS/cm. Results show that rather than a threshold response to salinity, small rises in salinity (from low levels) can produce increased growth and reproduction until a maximum is reached. Beyond this salinity, further increases result in a decrease in growth and reproduction. Studies on the growth of freshwater invertebrates and fish have generally shown a similar lack of a threshold response. The implications for assessing the effects of salinisation on freshwater organisms need to be further considered.
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