Linking mechanistic and behavioral responses to sublethal esfenvalerate exposure in the endangered delta smelt; Hypomesus transpacificus (Fam. Osmeridae)

Abstract

BackgroundThe delta smelt (Hypomesus transpacificus) is a pelagic fish species listed as endangered under both the USA Federal and Californian State Endangered Species Acts and considered an indicator of ecosystem health in its habitat range, which is limited to the Sacramento-San Joaquin estuary in California, USA. Anthropogenic contaminants are one of multiple stressors affecting this system, and among them, current-use insecticides are of major concern. Interrogative tools are required to successfully monitor effects of contaminants on the delta smelt, and to research potential causes of population decline in this species. We have created a microarray to investigate genome-wide effects of potentially causative stressors, and applied this tool to assess effects of the pyrethroid insecticide esfenvalerate on larval delta smelt. Selected genes were further investigated as molecular biomarkers using quantitative PCR analyses.ResultsExposure to esfenvalerate affected swimming behavior of larval delta smelt at concentrations as low as 0.0625 μg.L-1, and significant differences in expression were measured in genes involved in neuromuscular activity. Alterations in the expression of genes associated with immune responses, along with apoptosis, redox, osmotic stress, detoxification, and growth and development appear to have been invoked by esfenvalerate exposure. Swimming impairment correlated significantly with expression of aspartoacylase (ASPA), an enzyme involved in brain cell function and associated with numerous human diseases. Selected genes were investigated for their use as molecular biomarkers, and strong links were determined between measured downregulation in ASPA and observed behavioral responses in fish exposed to environmentally relevant pyrethroid concentrations.ConclusionsThe results of this study show that microarray technology is a useful approach in screening for, and generation of molecular biomarkers in endangered, non-model organisms, identifying specific genes that can be directly linked with sublethal toxicological endpoints; such as changes in expression levels of neuromuscular genes resulting in measurable swimming impairments. The developed microarrays were successfully applied on larval fish exposed to esfenvalerate, a known contaminant of the Sacramento-San Joaquin estuary, and has permitted the identification of specific biomarkers which could provide insight into the factors contributing to delta smelt population decline.

Predation on Fishes in the Sacramento-San Joaquin Delta: Current Knowledge and Future Directions

“…Much more research is needed on the behavioral effects of contaminants on Delta fishes, because little is known about these effects (but see Connon et al 2009Connon et al , 2011McIntyre et al 2008McIntyre et al , 2012. There are some extant data for other related species and these likely can be use to gain insights on predator-prey interactions of Delta fishes.…”

Hepatic Proteome Sensitivity in Rainbow Trout after Chronically Exposed to a Human Pharmaceutical Verapamil

“…In the present study, hyperosmotic glycine-rich protein was identified as significantly down-regulated by 42 days of exposure to higher concentrations of VRP in fish liver. Osmoregulation is physiologically controlled by chemical messages from the endocrine system, along with cell signaling and nerve transmission (40). The Ca 2ϩ antagonists have been suggested to induce osmotic imbalances in fish (41) that are linked to effects on ATPase activity responsible for maintaining the sodium transmembrane electrochemical gradient (42).…”

Is Extinction Inevitable for Delta Smelt and Longfin Smelt? An Opinion and Recommendations for Recovery

“…Contaminants have been considered one of the important stressors for Delta Smelt (IEP-MAST 2015); however, the lack of a direct empirical measure of impact on fish abundance has made this factor difficult to assess. Importantly, laboratory studies using Delta Smelt have demonstrated that ambient Delta waters result in a variety of measurable impacts to Delta Smelt gene regulation, physiology, growth and fitness (Connon et al 2009(Connon et al , 2012Hasenbein et al 2014;Hammock et al 2015;Jeffries et al 2015), making this a critical topic to include in future study and manage decision-making.…”