Effects of temperature on standard metabolic rate, hypoxia tolerance, and critical thermal maxima in invasive cichlids

Abstract Objective Jaguar Guapote Parachromis managuensis and Red Devil/Midas cichlids Amphilophus spp. are highly invasive species in the family Cichlidae native to Central America. These cichlids are popular within the aquarium trade, leading to their broad introduction outside of their native range. Information about potential environmental plasticity of a species can improve predictions of invasion potential. In this respect, measures of environmental influences on metabolic rate and hypoxia tolerance are important for understanding limitations in adaptability and subsequently guiding the management of invasive species. Methods Standard metabolic rate (SMR), hypoxia tolerance, and critical thermal maxima (CTmax) were compared between Jaguar Guapote and Amphilophus spp. For SMR and hypoxia tolerance, a range of temperatures spanning subtropical to tropical environments (i.e., 22, 28, and 34°C) was used, followed by stepwise decreases in oxygen saturation until loss of equilibrium. Results Jaguar Guapote and Amphilophus spp. both had lower SMR at 28°C than at 34°C, SMR at 22°C was not different from either temperature. Both Jaguar Guapote and Amphilophus spp. were the most sensitive to hypoxia at the coolest temperature (22°C) relative to warmer temperatures (28°C and 34°C). Upper thermal tolerance (CTmax) was similar between species (∼42°C), although Jaguar Guapote were more resilient based on a higher agitation temperature and recovery following high temperature exposure. Conclusions These results indicate temperatures that are representative of their natural distribution (i.e., near 28°C) offer energetic savings for Jaguar Guapote and Amphilophus spp. relative to warmer temperatures (34°C), with cooler temperatures (22°C) having higher metabolic costs than expected. Both Jaguar Guapote and Amphilophus spp. are sensitive to hypoxia at cooler temperatures (22°C). Therefore, these species are relatively resilient to high temperatures, but low temperatures may restrict their invasiveness.