Length and Weight Reduction in Larval and Juvenile Yellow Perch Preserved with Dry Ice, Formalin, and Ethanol

Abstract

Due to the increasing interest in biochemical indices such as the RNA–DNA ratio used to measure fish growth, fish often need to be stored frozen with dry ice (i.e., −80°C). The objectives of this study were to (1) quantify the effects of dry ice on both the length and weight of larval and juvenile yellow perch Perca flavescens preserved for storage periods of 15 d and 7–8 months, (2) compare these effects with those of two commonly used preservatives (a 10% solution of formalin and a 75% solution of ethanol), and (3) provide equations to convert the lengths and weights of larval and juvenile yellow perch preserved with dry ice, formalin, and ethanol back to their initial unpreserved values. For all preservation methods, fish weight was more affected than length. The smallest length reduction was observed with formalin (short term: 2.1% and 0.1% for larvae and juveniles, respectively; long term: 10.1% and 1.2%), followed by dry ice (short term: 4.0% and 1.4%; long term: 7.2% and 3.9%) and ethanol (short term: 9.6% and 1.2%; long term: 11.7% and 1.2%). The smallest weight reduction was also observed with formalin (short term: 21.9% and 2.2%; long term: 23.2% and 3.9%), followed by dry ice (short term: 54.0% and 11.1%; long term: 52.8% and 8.4%) and ethanol (short term: 61.1% and 22.0%; long term: 66.0% and 26.0%). Except for one case, all of the regression equations that were built to convert the lengths and weights of larval and juvenile yellow perch preserved with dry ice, formalin, and ethanol back to initial measurements were highly significant.