Thermal response of demersal and pelagic juvenile fishes from the surf zone during a heat-wave simulation

Abstract

Experimental measurements were collected in the laboratory to evaluate the maximum thermal limit and thermal plasticity of Neotropical juvenile fish with different life habitats (demersal and pelagic) from surf zone in response to a “heat-wave experiment”. Trials were conducted using two temperature acclimations (Ta), including the current average temperature of Southeastern Brazil (Ta: 14 days at 25°C) and the “heat-wave experiment” (Ta: 14 days at 30°C), simulating a heat-wave event that occurs when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5°C. Typical species of the surf zone were used: the demersal White sea catfish (Genidens barbus) and Gulf kingcroaker (Menticirrhus littoralis), and the pelagic fishes Great pompano (Trachinotus goodei) and Long-fin mullet (Mugil brevirostris). The thermal range and plasticity values for the both life-habitats species were verified through current and heat-wave acclimation. The thermal tolerance at high temperatures (CTmax) of these species differed between Ta, habitat and species. Fish showed a species-specific response to temperature increase, regardless of their habitat even under similar abiotic conditions. However, at the heat-wave simulation, the demersal fish presented a greater thermal plasticity in relation to the pelagic fish. Despite the higher thermal tolerance when exposed to heat-wave simulation, all fish species displayed a lower thermal edge safety that is markedly close to their maximum thermal limits.