Determination of thermal tolerance parameters of swordtail (Xiphophorus helleri) and platy fish (X. maculatus) acclimated to different temperature levels

Thermal tolerance parameters of swordtail (Xiphophorus maculatus) and platy (X. helleri) at three acclimation temperatures were determined in the study. The CTMin values at 20, 24 and 28°C acclimation temperature were 9.41,10.42 and 11.95°C respectively for platy and 9.38,11.5 and 13.23°C for swordtail, while CTMax values were 37.41, 39.19 and 40.52°C for platy and 36.94, 38.89 and 40.07°C for swordtail. Accordingly, acclimation temperature affected the lower and upper temperature tolerances of fish by 3-4 °C. The CTMin ARR values varied between 0.42-0.42 in swordtail and 0.20-0.34 in platy, while CTMax ARR ranged between 0.29-0.48 in swordtail and 0.33-0.44 in platy depending on acclimation temperature. Thermal tolerance polygon area of platy (232°C2) was slightly higher than that of swordtail (217.3°C). The fact that both fish species have lower temperature tolerances limits their geographic distribution and aquaculture in subtropical climates where the water temperature drops to 10°C in winter.