Dry mass estimation of tropical aquatic insects using different short-termpreservation methods

Relationships of body mass and head capsule width were calculated for Thrau lodes sp., Haplohyphes sp. (Ephemeroptera), Leptonema sp. and Nectopsyche s p. (Trichoptera), and Anacroneuria sp. (Plecoptera) using different preserv atives (Freezing; Formaldehyde 4% and Kahle). The organisms were collected monthly during a year on the Orituco river, Venezuela with a Surber net (0. 1296 m(2) and 0.286 mm mesh size). The data presented here are representat ive of the organism conditions year around. No attempt was made to quantify intersample variation. Regression analysis indicated that all relationship s were highly correlated for any of the fixatives used. Changes in dry mass per unit change of head capsule width, vary among species and preservative s with no clear relationship among them. Changes in dry mass calculated as the difference between dry mass of preserved samples to those of unpreserve d ones, indicate that all fixatives underestimate dry mass by as much as 85 .4%, except for Nectopsyche sp. whose dry mass was always overestimated. Th ese results provide further evidence on the effect of preservatives on dry mass losses. Even when working with tropical species, any study in which bi omass is going to be determined should consider the effect of preservatives on dry mass.