How Much Cleaning is Needed When Processing Otoliths from Fish Larvae for Microchemical Analysis?

Abstract

Otolith microchemistry is a widely used tool in fish ecology and fisheries management. Cleaning-protocol assessments are lacking, however, especially for larval fish otoliths, which are more fragile and difficult to manipulate than larger otoliths. Herein, we assess the value of cleaning larval fish otoliths with sonication, a commonly used technique that is time consuming and risks loss or breakage of small otoliths, as well as with a lesser-known technique using a low-power laser cleaning pulse (LPLCP). We measured trace elements in larval Walleye Sander vitreus reared in different water strontium concentrations. Strontium and Ba did not differ among any cleaning treatments, indicating that neither sonication nor a LPLCP is necessary. Likewise, Mn did not differ between sonicated and nonsonicated treatments; however, Mn was lower when a LPLCP was used. We suggest omitting the sonication step when preparing otoliths for trace element analysis of Sr, Ba, Mn, and other trace elements found in high abundances. The addition of a LPLCP is useful, although more research in this arena is warranted. Our findings should greatly reduce otolith processing time and the risk of losing and breaking larval otoliths during the cleaning process.

Received July 29, 2013; accepted January 21, 2014

ACKNOWLEDGMENTS

We thank the Ohio Division of Wildlife, Konrad Dabrowski, and Kyle Ware for their help with Walleye collection and spawning. Elemental analysis of otoliths was done by Anthony Lutton and the Ohio State University Trace Elemental Research Laboratory. We also thank Alex Johnson and the rest of the Ohio State University's Aquatic Ecology Laboratory for assistance in the laboratory.