Peter J. Allen | Search USGS

USGS2026

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

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 (CT max ) 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 (CT max ) 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.

Transactions of the American Fisheries Society↗

USGS2025

Trophic assessment of potential competition between invasive cichlids and sport fish in Puerto Rico reservoirs

Objective Several species of New World cichlids have recently invaded reservoirs in Puerto Rico, potentially jeopardizing established recreationally important, albeit nonnative, sport fish populations. Interactions between invasive species and important sport fish must be understood so that they can be mitigated when feasible. This study compared monthly prey consumption between three invasive cichlids (Jaguar Guapote Parachromis managuensis and two species of Amphilophus ) and two principal sport fishes (Largemouth Bass Micropterus nigricans and Butterfly Peacock Bass Cichla ocellaris ) to understand potential for competitive interactions. Methods Stomach contents were evaluated quarterly using gastric lavage for sport fish and destructive sampling techniques for invasive species. Prey proportion by mass was calculated for each individual, and mean prey proportion by mass was calculated for each species by reservoir, month, and overall. Multivariate hypothesis testing using permutational multivariate analysis of variance and visualization of potential diet overlap were performed via analysis of variance and nonmetric multidimensional scaling (NMDS), respectively. Results Fish were the most common prey type, and Threadfin Shad Dorosoma petenense was the most prevalent prey species. Although there were significant differences in diets of invasive cichlids and sport fishes ( P < 0.01), there also was considerable overlap based on low percentages of variation in diets explained by species (3–19% < pseudo- R 2 ) and NMDS visualizations. Diets varied little across reservoirs and months (≤4% pseudo- R 2 ; high overlap in NMDS space). Conclusion These data indicate that the diet of Jaguar Guapote and Amphilophus spp. may overlap with that of sport fish populations in Puerto Rico. Jaguar Guapote relied on Threadfin Shad more than other species, with Amphilophus spp. relying more on detritus and noncrayfish invertebrates. Thus, if prey are limited, Jaguar Guapote may have a more direct effect via competition for prey. Finally, we report evidence of Largemouth Bass recruitment failure and local extirpations that support a hypothesis that invasive cichlids are having negative effects on at least Largemouth Bass, although the mechanism is unclear.

Puerto Rico↗