An Evaluation of Fish Tissue Monitoring Alternatives for Mercury and Selenium: Fish Muscle Biopsy Samples Versus Homogenized Whole Fillets

Analysis of Selenium in Fish Tissue: An Interlaboratory Study on Weight Constraints

Environmental monitoring programs that target fish tissues for selenium (Se) analysis present unique sampling and analytical challenges. Selenium monitoring programs ideally focus on egg/ovary sampling but frequently sample multiple tissues with varying lipid content, often target small-bodied fish species because of their small home ranges, and require reporting in units of dry weight. In addition, there is a growing impetus for nonlethal tissue sampling in fish monitoring. As a result, Se monitoring programs often generate low-weight tissue samples of varying lipid content, which challenges analytical laboratories to quantify tissue Se concentrations accurately, precisely, and at desired detection limits. The objective of the present study was to stress-test some conventional analytical techniques used by commercial laboratories in terms of their ability to maintain data quality objectives (DQOs) in the face of sample weight constraints. Four laboratories analyzed blind a suite of identical samples, and data were compared against a priori DQOs for accuracy, precision, and sensitivity. Data quality tended to decrease with decreasing sample weight, particularly when samples were less than the minimum weights requested by the participating laboratories; however, effects of sample weight on data quality were not consistent among laboratories or tissue types. The present study has implications for accurately describing regulatory compliance in Se monitoring programs, highlighting some important considerations for achieving high data quality from low-weight samples. Environ Toxicol Chem 2023;42:2119-2129. © 2023 SETAC.

Comparison of Two Total Mercury Screening and Assessment Methods in Fishes: Biopsy Punch and Dried Muscle Samples

Rapid and effective quantification of total mercury concentrations ([THg]) in fish muscle is an important part of ongoing monitoring to provide reliable and near real-time public health guidance. Methods for quantifying THg in fish muscle frequently require the use of large sample mass and numerous preparation steps. Wet (aka fresh weight) biopsy punch samples of fish muscle have been used to quantify THg directly, without drying and homogenization. Both methods have advantages and disadvantages. We compare the use of fresh weight biopsy punches for quantifying THg to using larger, dried homogenized samples. The [THg] determination for the two sampling methods was EPA method 7473. Three separate biopsy punch samples and a large muscle sample were taken from each fish and analyzed on a Direct Mercury Analyzer. There were no statistical differences between mean log transformed wet weight [THg] from biopsy punches and homogenized muscle across all samples or within individual species. Similarly, across the range of [THg] (7.5-612.7 ng/g ww), linear regression of [THg] from biopsy punch and homogenized muscle samples was not different from a 1:1 linear relationship. Linear regression statistics of [THg] with fish fork length produced similar results for both biopsy punch and homogenized muscle samples. However, the coefficient of variation among biopsy punch replicates for individual fish was frequently above the acceptable threshold of 15%. We recommend biopsy punches be used as an effective tool for broad-scale rapid monitoring of fish resources for Hg, while homogenized muscle samples be used for fine-scale ecological and health questions.

Non-Lethal Sampling Supports Integrative Movement Research in Freshwater Fish

Freshwater ecosystems and fishes are enormous resources for human uses and biodiversity worldwide. However, anthropogenic climate change and factors such as dams and environmental contaminants threaten these freshwater systems. One way that researchers can address conservation issues in freshwater fishes is via integrative non-lethal movement research. We review different methods for studying movement, such as with acoustic telemetry. Methods for connecting movement and physiology are then reviewed, by using non-lethal tissue biopsies to assay environmental contaminants, isotope composition, protein metabolism, and gene expression. Methods for connecting movement and genetics are reviewed as well, such as by using population genetics or quantitative genetics and genome-wide association studies. We present further considerations for collecting molecular data, the ethical foundations of non-lethal sampling, integrative approaches to research, and management decisions. Ultimately, we argue that non-lethal sampling is effective for conducting integrative, movement-oriented research in freshwater fishes. This research has the potential for addressing critical issues in freshwater systems in the future.