Thermal tolerance parameters of thirteen ornamental fish species (Carassius auratus, Cyprinus carpio: koi, Brachydanio rerio, Puntius tetrazona, Garra rufa, Poecilia latipinna, P. reticulata, Pterophyllum scalare, Labidochromis caeruleus, Cyrtocara moorii, Carydoras paleatus, Trichogaster trichopterus and Hypostomus plecostomus) at three acclimation temperatures (20, 24 and 28 degrees C) were determined in this study. The CTMin values of the species ranged from 2.55-6.54 degrees C (C. auratus) to 11.66-13.94 degrees C (P. tetrazona), while CTMax values ranged from 33.91-37.51 degrees C (P. cory) to 39.71-41.80 degrees C (P. reticulata). The acclimation response ratio (ARR) values between 20 and 28 degrees C acclimation temperature (AT) ranged from 0.18 (H. plecostomus) to 0.63 (B. rerio) for CTMin, while these values ranged between 0.17 (G. rufa) and 0.67 (P. tetrazona) for CTMax values. Thermal tolerance polygon was widest in C. auratus (281 degrees C-2) and narrowest in P. tetrazona (188 degrees C-2). Despite being in the same family (Cyprinidae), it is interesting and unusual that C. auratus is a typical eurythermal and P. tetrazona is a typical stenothermal species. C. auratus and C. carpio followed by G. rufa, P. latipinna and B. rerio are the species which are advantageous in terms of aquaculture due to their wide temperature tolerance range and high ARR values.