Richard E. Connon

Objective This study aims to develop the culture methods for Longfin Smelt Spirinchus thaleichthys in a laboratory setting, achieving the first production of a fully captive second generation (F2). The objective includes understanding the critical factors influencing the breeding and maturation of this species in captivity, contributing to conservation efforts and potential revival of this threatened species. Methods Longfin Smelt broodstock were collected from the San Francisco Estuary and reared in controlled conditions at the University of California Davis Fish Conservation and Culture Laboratory (FCCL). The study involved spawning of wild broodstock, rearing of first generation (F1) progeny to adulthood, and subsequent spawning to produce F2 offspring. Key variables such as salinity, temperature, and diet were carefully managed throughout the process. Fertilization and hatching rates were calculated, and the larvae were reared using the same methods to closely monitor and understand their growth and development. Result First generation Longfin Smelt successfully matured and spawned at age 1, earlier than commonly observed in the wild. From five crosses, four produced viable offspring. The study recorded a range of fertilization rates (10–40%) and high hatching rates (75–97%). Salinity was identified as a critical factor in both larval development and adult maturation. While initial larval survival was challenging, the larval rearing system used in this study proved effective. Conclusion The study represents a major breakthrough in the cultivation of Longfin Smelt, showing that it is possible to complete their life cycle under controlled conditions. It has provided valuable understanding of the maturation and breeding processes in these fish, with an emphasis on the influence of salinity. These outcomes are crucial for conservation strategies, offering the potential to help establish a refuge population and laying the groundwork for further research aimed at refining captive breeding methods for this species.

Pesticides with novel modes of action including neonicotinoids and anthranilic diamides are increasingly detected in global surface waters. Little is known about how these pesticides of concern interact in mixtures at environmentally relevant concentrations, a common exposure scenario in waterways impacted by pesticide pollution. We examined effects of chlorantraniliprole (CHL) and imidacloprid (IMI) on the sensitive invertebrate, Daphnia magna. Exposures were first performed using surface waters known to be contaminated by agricultural runoff. To evaluate the seasonal variation in chemical concentration and composition of surface waters, we tested surface water samples taken at two time points: during an extended dry period and after a first flush storm event. In surface waters, the concentrations of CHL, IMI, and other pesticides of concern increased after first flush, resulting in hypoactivity and dose-dependent photomotor responses. We then examined mortality and behavior following single and binary chemical mixtures of CHL and IMI. We detected inverse photomotor responses and some evidence of synergistic effects in binary mixture exposures. Taken together, this research demonstrates that CHL, IMI, and contaminated surface waters all cause abnormal swimming behavior in D. magna. Invertebrate swimming behavior is a sensitive endpoint for measuring the biological effects of environmental pesticides of concern.