Responses of Showy Leopard Frog Larvae (Lithobates spectabilis) to the Presence of Introduced Rainbow Trout in Mexico

The introduction of invasive fish for aquaculture can significantly impact native aquatic fauna, especially in regions where native amphibians have a biphasic life cycle. We conducted three laboratory experiments to assess the effects of introduced rainbow trout (Oncorhynchus mykiss) aquaculture on the native showy leopard frog (Lithobates spectabilis) in Mexico. We aimed to understand the effects of trout visual and chemical cues on tadpole behaviour, and the long-term effects of chemical cues (in interaction with tadpole density) on tadpole growth, development and survival. In Experiment 1, we exposed groups of tadpoles to the visual cue of a trout, comparing their refuge use and position within the tank to a control group. In Experiment 2,we exposed groups of tadpoles to trout chemical cues contrasting their refuge use to a control group. In Experiment 3, we exposed tadpoles at different densities to trout chemical cues for a prolonged period, recording their growth, development and survival. Results showed that tadpoles did not alter refuge use in response to trout visual cues but positioned themselves farther from these cues compared to controls. Tadpoles increased refuge use in response to chemical cues. Long-term exposure to chemical cues did not affect tadpole growth, development or survival, but higher densities led to lower survival rates. Our findings suggest that trout farming, through fish escapement or untreated farm water discharge containing trout chemical cues, could trigger behavioural responses in L. spectabilis larvae, increasing refuge use and local tadpole densities, ultimately compromising their survival and, potentially, species persistence.