Some Factors Affecting on Dry Weight,Organic Weight and Concentrations of Carbon and Nitrogen in Freshly Prepared and in Preserved Zooplankton

Effects of rinsing and preservation on dry weight, organic weight, and chemical composition were determined on the chaetognath Sagitta nagae and the copepods Calanus sinicus, Pleuromamma xiphias and Acartia tonsa. Samples rinsed with distilled water were always lighter than comparable samples rinsed with seawater, showing apparent decrease in the organic matter and chemical contents (as total carbon and nitrogen) by weight; these losses increased with increasing volume of the rinse water. The volume of distilled water used for rinsing should be less than 0.3 ml per 1 mg dry weight of sample in order to avoid the significant loss of body substances. Isotonic ammonium formate rinse often resulted in the widest range of variation and on an average the organic weight and chemical contents were slightly lower than those of fresh samples rinsed with filtered seawater. Freeze-drying samples resulted in dry and organic weights as well as chemical compositions that were somewhat greater than oven-dried samples. The organic matter and chemical contents by weight decreased significantly within 2.5 days of being placed in Borax-buffered formaldehyde-sea water solution. Loss of organic weight from fresh samples exceeded 20% after one week of the preservation. Hexamine-buffered formaldehyde solution showed a result which was different from the Borax-buffered solution.