Changes in size and weight of two species of planktonic hydromedusae following preservation in 10% v/v formalin-seawater solution were measured over 154 days. Umbrella mean diameter was reduced to an average of 67.8% and 84.9% of the initial size depending on species; for both species
stabilization was achieved after 60 days. Mean wet weights after 154 days corresponded to 30.5% and 37.9% of the initial fresh weight; no stabilization was achieved over that time period. Changes in body dimensions and weight varied significantly between species and appeared to depend on their
morphology. Best fitted equations are presented to predict the percent shrinkage for both species over time. The dry weight/wet weight ratios of preserved animals were similar to those of fresh specimens suggesting that preservation does not affect this ratio. We recommend that correction
factors be based on animal umbrella diameter; animal weight then can be estimated from weight-diameter relationships established for fresh animals. Umbrella measurements of preserved specimens should be taken after a minimum of 60 days.
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