UC Davis

We investigated the physiological response of the endangered Tidewater Goby Eucyclogobius newberryi to the presence of Threespine Sticklebacks Gasterosteus aculeatus (native to California) and Rainwater Killifish Lucania parva (nonnative). A fully factorial experimental design was used to examine species assemblage effects on juvenile fish over a 28-d period. Growth characteristics (weight, SL, and relative condition factor [Kn]) and stress hormone levels (cortisol) were assessed under ample food conditions and at a salinity of 15‰. Weight and SL of Tidewater Goby increased throughout the experiment; growth did not differ in relation to fish assemblage treatment, but significant differences in growth were observed between sampling dates within the experiment. Rainwater Killifish exhibited marginal increases in weight, SL, and Kn, but these increases were not different among assemblage treatments or over time. For Threespine Sticklebacks, weight and SL increased during the final 2 weeks of the experiment, resulting in significant differences over the entire experimental period; however, growth characteristics of this species did not differ among assemblage treatments. Cortisol levels in all three species were not significantly affected by assemblage treatment. The present results indicate that juvenile Tidewater Goby are not adversely affected by native Threespine Sticklebacks or nonnative Rainwater Killifish under stable abiotic conditions in the absence of food limitation. Received March 6, 2015; accepted September 24, 2015