Relationships in selenium concentrations among fish tissues to support selenium assessments and regulations

Selenium (Se) toxicity to fish is primarily manifested via maternal transfer to the eggs. Several regulatory jurisdictions have adopted Se criteria or guidelines expressed as the Se concentration in fish eggs (typically expressed as egg/ovary Se concentrations, thereby suggesting these are equivalent). Because it is not always feasible to sample fish eggs or ripe ovaries at a site, it can be necessary to sample muscle or whole-body (WB) tissue. This study evaluated whether there were consistent relationships in tissue Se concentration within and across fish species. Additionally, based on findings in a companion study, we evaluated whether ovary Se concentrations are inversely related to oocyte development in a wide range of fish species. Consistent with the companion study, the spawning status of the wide range of fish species had a significant influence on Se concentrations, with Se concentrations in eggs and ripe ovaries typically lower and less variable than those in unripe ovaries. Considering Se data for eggs|ripe ovaries, there was a consistent relationship with muscle or WB Se over a wide range of fish species. Additionally, for a majority of fish species, the relationships between egg|ripe ovary Se concentrations versus muscle and WB Se concentrations had slopes significantly different than 1, indicating that single-tissue Se ratios are not applicable over a broad range of muscle or WB Se concentrations. Considering these findings, we recommend future studies clearly report whether eggs or ovaries were sampled and provide other diagnostic measures of reproductive status such as the gonado-somatic index. We also conclude direct comparison of Se concentrations from unripe ovaries to egg Se thresholds is not appropriate.