Thermal Tolerance and Metabolism of Archocentrus nigrofasciatus Acclimated to a Large Daily Temperature Fluctuation Reflect its Success as an Invasive Species

Abstract

Fish exhibit thermal tolerance and metabolism correlated to recent thermal history, and more studies should examine species’ responses to large fluctuations in daily temperatures. We compared thermal tolerance and metabolic responses between fish acclimated to constant temperatures and a large, daily thermal cycle of 10°C. Black Convict cichlid (Archocentrus nigrofasciatus) is a freshwater teleost native to Central America, with non‐native populations established in numerous locations. Black Convict cichlid were acclimated for two weeks to constant 20°C or 30°C, or a daily cycle of 20–30°C (“cycling group”, ~0900–1500 hrs). Following acclimation, routine metabolism (oxygen consumption, Mo2) and Critical thermal maxima/minima (CTmax/CTmin) were measured. Critical thermal limits were compared via ANOVA, with the cycling group sampled from both the daily minimum at 20°C (0900 hrs) and daily maximum at 30°C (1600 hrs). CTmax (0.3°C per degree of acclimation) and CTmin (0.4 °C per degree of acclimation) increased with acclimation. CTmax for the cycling group were 0.7°C higher when sampled from the maximum 30°C (39.3°C) of the daily cycle compared to 20°C (38.6°C). CTmin values for the cycling group were 2.2°C higher when sampled from the maximum 30°C (14.6°C) of the daily cycle compared to 20°C (12.4°C). Mo2 was measured acutely at 20°C and 30°C for each acclimation group, with the cycling group sampled from the daily minimum at 20°C (0900 hrs) and daily maximum at 30°C (1600 hrs). ANOVA showed that mass‐specific Mo2 decreased with increasing acclimation temperature for fish measured acutely at 30°C, where fish acclimated to 20°C (Mo2 = 0.329 mg/h/g) demonstrated an 84% higher Mo2 than fish acclimated to 30°C (Mo2 = 0.178 mg/h/g). Mass‐specific Mo2 also decreased with increasing acclimation temperature for fish measured acutely at 20°C, where fish acclimated to 20°C (Mo2 = 0.170 mg/h/g) demonstrated a 139% higher Mo2 than fish acclimated to 30°C (Mo2 = 0.071 mg/h/g). Mo2 was measured continually across the 24h daily thermal acclimation cycle of 20 – 30°C for all groups. Total oxygen consumption across the 24h cycle was highest for the constant 30°C group naively exposed to the cycle and lowest for the cycling group. Black Convict cichlid retains more upper thermal tolerance than lower thermal tolerance with altered thermal acclimation, and this hardy species shows metabolic compensation following high temperature acclimation (30°C) and large, daily cycling temperature acclimation (20 – 30°C). These aspects of fish thermal physiology phenotypes are reflective of a successful invasive fish species that may respond more robustly to impacts from anthropogenic climate change.Support or Funding InformationFunding was provided through startup funds to JE from CSUSM.