Short‐Term Effects of Formalin and Ethanol Fixation and Preservation Techniques on Weight and Size of Fish Eggs

Abstract

AbstractPreservative‐induced changes in the weight and size of fish eggs distort information in studies of fecundity and egg production, but the nature of changes that occur during short‐term preservation is not well understood. To determine the nature of these effects and to provide a basis for correcting for such changes after sample processing, we examined the short‐term effects of 10% formalin and 70% ethanol on eggs from gravid female white suckers Catostomus commersonii and fantail darters Etheostoma flabellare collected in two tributaries of the New River, Virginia. A sequential treatment with formalin and then ethanol was also tested to simulate effects expected in a typical fixation and preservation schedule when eggs are fixed and preserved within the fish. Formalin resulted in a significant gain (36%) in egg dry weight during the first 12 h of treatment. Ethanol had no detectable effect on egg dry weight after 9 d of fixation and preservation. Eggs that were fixed in formalin and then preserved in ethanol showed dry weights that were equivalent to those of eggs that were fixed and preserved only in ethanol, implying a reversal of the effect of formalin. We hypothesize that the action of ethanol on egg proteins unbinds the formaldehyde, with the effect of reversing formalin‐induced weight gain in eggs that have been fixed with formalin. Reductions in egg diameter were similar (∼17% after drying) between ethanol and formalin treatments, but there was an additional 5.4% shrinkage when eggs were fixed in formalin and then preserved in ethanol. In comparison with changes in egg diameter, changes in egg weight had a wider range among treatments and less variability within treatments. The experimental results indicate that egg weight is a more reliable indicator of preservation‐induced changes and a more consistent characteristic than egg diameter for comparing egg production among fishes.