Native and invasive cichlid fish respond differently to thermal challenge

Global warming affects aquatic organisms by increasing water temperature, which leads to changes in numerous abiotic and biotic factors. The combined effects of habitat warming and biological invasions pose a serious risk to native fish, especially if native species are more sensitive to warming than invasives. In this work, we evaluated whether increasing water temperature affects the behaviours of swimming activity, aggressive interactions, capture attempts, prey consumed and foraging efficiency of the native Mexican mojarra and the invasive convict cichlid. To do this, we exposed 20 juveniles of each species to either a constant water temperature treatment at 28°C for 15 days (control group) or to a gradual increase in temperature from 28°C to 35°C over the same period (treatment group). In both species, individuals in the group exposed to experimental warming had lower swimming activity than those in the control group and in the convict a higher number of aggressive interactions than those in the control group. However, the species showed opposing effects of warming on feeding-related behaviours: in the Mexican mojarra, the number of capture attempts, prey consumed and capture efficiency were higher in the group exposed to thermal increase than in the control group, whereas in the convict cichlid, these behaviours were lower in the treatment group than in the control group. Thus, the convict cichlid showed stronger potentially adverse effects of habitat warming than the Mexican mojarra in behaviours associated with foraging. This is the first comparison of the behavioural effects of habitat warming between invasive and native cichlid fishes. Other studies of the ecological implications of habitat warming in the Amacuzac River are necessary to support the conservation of the native Mexican mojarra in the presence of the invasive convict cichlid.