Effects of copper exposure on the olfactory response of Delta smelt (Hypomesus transpacificus): Investigating linkages between morphological and behavioral anti-predator response

Delta Science Fellowship 2020

Fellow: Pedro Alejandro Triana Garcia, PhD Student, UC Davis
Research mentor: Swee J Teh, University of California, Davis
Community mentors: Shawn Acuña, Metropolitan Water District of Southern California

Why this research matters

Delta smelt population has declined dramatically to the point to be declared as a critically endangered
fish. One hypothesis for the recent decline is that pollutants can disrupt the fish’s sensory ecology and
make them more susceptible to predation. Since fish rely on their olfactory system to assess predation
risk and avoid predators this could have serious consequences on the survival of the species. The study
of the olfactory biology of delta smelts and the effects of a common water pollutant (copper) on its
sensory ability will help to further our understanding on the biology and conservation of this endangered fish.

Project

This study aimed to address the question of how water-borne copper can affect the ability of delta smelt
to detect predator related odorants and conduct essential behaviors. To do this, the project included a
thorough morphological and cytological study of the delta smelt olfactory organ, which had previously
not been well-studied. The researchers also characterized the olfactory mediated antipredatory response to alarm cues and assessed the effects of copper exposure on the anti-predator behavior and morphology of the olfactory rosette of delta smelt.

Results

Delta smelts have a highly sophisticated and sensitive olfactory system. They can assess the likelihood of
being predated based on the concentrations of alarm cues in the water and behave accordingly to avoid
predation risk. In other words, they can smell “danger.” Delta smelts are highly susceptible to water-borne copper and showed morphological alterations in the olfactory organ and impairment of their olfactory-mediated anti-predatory behavior upon exposure to low concentrations of copper which can be found in the San Francisco Estuary. To enable these analyses, the study included the basic morphological and physiological research necessary to assess the impacts of copper on the delta smelt’s olfactory response. The project produced a morphologic characterization of the delta smelt olfactory organ, and a standardized odorant-response curve which will allow researchers to use behavioral studies to assess olfactory-mediated anti predatory response.

Management Applications

This project improves our understanding of basic anatomy and behavior of delta smelt, as well as specific findings on the impact of copper pollution on this endangered species. The anatomical and behavioral findings lay an important groundwork for future applied research on pollutants and other stressors, while the research on copper exposure provides information that can be used by managers of the state and federal agency and the Interagency Ecological Program to better prioritize the mechanistic and ecological effects of pollutants in the San Francisco Estuary. This project was shared in the state of the San Francisco estuary conference with managers from different institutions.

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