Effects of Ethanol Preservation on Larval and Fingerling Walleye and Gizzard Shad Body Size

Abstract

Characterizing larval fish dynamics helps identify factors contributing to poor or strong recruitment events and informs stocking practices. Growth is fundamental to fish ontogeny and survival, especially during critical early life stages, which can depend heavily on access to prey. However, obtaining accurate body size measurements of larval fish in the field can be challenging and often means samples must be preserved for later analysis. Importantly, this process can affect fish size. Here, we examined the effects of preservation in 95% ethanol on the total lengths (mm) and wet weights (mg) of larval and fingerling Walleye Sander vitreus and Gizzard Shad Dorosoma cepedianum collected from the field using pushed ichthyoplankton nets. We also estimated the time required for preservation effects to stabilize. Responses to preservation were similar between species, with consistent decreases in wet weights of ~40–70% depending on fish size, which took ~2 months to stabilize. Conversely, the response of total length was variable in direction, with lengths increasing or decreasing up to 5–10%. As a result, the average effect of preservation on total length was minimal (<2.5% decreases). Walleye and Gizzard Shad body size play an important role in understanding their dynamics early in life, and the effects of preservation should be considered to accurately and precisely characterize size metrics.