Determination of critical thermal limits for doctor fish, Garra rufa Heckel 1843

In this thesis, we aimed to determine the critical thermal minimum (CTMin), critical thermal maximum (CTMax) values, thermal tolerance polygon, acclimation response ratio (ARR) values and thermal tolerance range in two different sizes of doctor fish (Garra rufa Heckel, 1843), small size (4.27 ± 0.13 cm and 0.85 ± 0.06 g) and large size (7.51 ± 0.19 cm 4.04 ± 0.30 g) had been acclimated to three acclimation temperatures (15, 25, 35 ± 0.5 °C) for one months. The critical minimum and maximum temperature limits (CTM) of the small and large size of doctor fish were determined by cooling or heating at the rate of 0.3 °C/min for randomly selected 20 fish from each acclimation groups. The lowest critical thermal limits (CTMin) were ranged between 3.04 ± 0.03 and 10.21 ± 0.19 °C for large size fish and 3.27 ± 0.11 to 10.88 ± 0.14 °C for small size fish. The upper critical thermal limit values (CTMax) were ranged between 36.99 ± 0.26 to 42.87 ± 0.06 °C in large fish and 35.51 ± 0.36 to 43.05 ± 0.09 °C in small fish groups. Acclimation response ratio (ARR) were ranged from 0.20 to 0.51 according to fish size and temperature range. The higher ΔCTM values led to increases in the acclimation response ratio. Calculated ARR values showed that both large and small fish were more tolerant to cold. The thermal tolerance polygon and area varied according to the acclimation temperatures and fish size. Thermal tolerance polygon are larger for large size fish. The values of the thermal tolerance polygon area are calculated as 638.35 °C2 for small size fish and 647.35 °C2 for big fish. Thermal tolerance ranges (TTR) generally ranged between 31.43-33.95 °C, while the highest thermal tolerance ranges are determined as 33.95 ° C in large size fish and 32.24 ° C in small size fish that acclimated to 15 °C water temperatures.