The aim of this study was to identify and assessthe growth retardation observed with increasing temperatures and led to economic losses at a rainbow trout (Oncorhynchus mykiss)farm at the Karaova Dam Lake within the province of Kirsehir, and to perform a poissonregression analysis and estimation on the effect of temperature. During the study, fish demonstrating signs of growth retardation were identified. For the studied rainbow trout, the value of the Pearson statistic was determined as 9.14, the deviation statistic as 7.53, and the artificial R 2 as 78.15, and the Chisquared goodness of fit as 21.11.Based on the poissonregression analysis, it was determined that temperature levels had an adverse effect on fish growth.