A Comparative Study on the Buoyancy of Resting Eggs from Different Artemia Populations, with Emphasis on Its Relationships with Habitat Salinity and Biometric Characters of Resting Eggs

The buoyancy of Artemia resting eggs is a feature with both biological and economic importance.Since the buoyancy of resting eggs is dependent on the specific weight of the eggs or salinity of ambient water,we suppose that habitat salinity may exert a selection pressure on resting egg buoyancy,and thereby lower habitat salinity may result in better floating capacity of resting eggs and vice versa.In this study,we compared the floating capacity of resting eggs from 25 Artemia populations.The results showed that the floating capacity of resting eggs varied greatly among different populations.The minimum salinity to float some eggs varied from 0 to 180.The salinity at which all resting eggs floated varied from 80 to 320.The FS_(50)(salinity with 50%eggs floating)of Zhundong and Yuncheng population was not detectable(over 50%eggs floating in distilled water),that of Kyêbxang Co population was 4.3,while the maximum value found in Dabancheng population was 234.5.In terms of the‘apparent specific weight’of resting eggs,18 populations exhibited a single-peak distribution pattern,while the other 7 populations showed a multiple-peak or non-peak distribution.Negative correlations were found between FS50 and chorion thickness,and between FS_(50) and the volume percentage of the chorion in eggs,supporting a previous standpoint that shell thickness was a determinative factor for the floating capacity of resting eggs.A positive correlation was determined between FS50 and habitat salinity.The hypothesis that habitat salinity may cause a directional selection on the buoyancy of resting eggs seems to be true.