UC Davis

Agricultural and urban contaminants enter aquatic environments at concentrations that can affect a variety of sublethal endpoints, including organismal behavior, which can in turn lead to impacts at the population level. The San Francisco Bay Delta (SFBD) is home to multiple threatened aquatic species, such as Delta smelt (Hypomesus transpacificus) and Longfin smelt (Spirinchus thaleichthys), with contaminant exposure likely playing a role in widespread population declines. Pesticides induce hyperactive or hypoactive states in these species, though little is known of the extent of hyperactivity that could be elicited by exposure to neurotoxic compounds. My study used pentylenetetrazole (PTZ), a γ-aminobutyrate (GABA) receptor antagonist, to explore hyperactive behavior in Delta smelt and Longfin smelt. I evaluated induced and spontaneous movement in light and dark conditions following exposure to increasing concentrations of PTZ. Delta smelt and Longfin smelt exposed to PTZ experienced changes in behaviors reflective of induced hyperactivity, including distance moved and swimming velocity, as well as spontaneous hyperactivity, such as time and frequency spent freezing, bursting, or entering the center of the arena (anti-thigmotaxis). The maximum hyperactivity for Delta smelt larvae was recorded following exposure to 8mM PTZ and for Longfin smelt larvae to 4mM PTZ. Together, this information not only confirms that PTZ could be used as a positive control in future behavioral toxicology studies for hyperactivity, but also provides for a better understanding of hyperactive behavior in these species of ecological concern.