Finfish cage aquaculture tends to increase breeding volumes (larger cages), so an increasing amount of fish is exposed to starvation before fishing. This thesis aims to determine the possibility of using biometric data to assess the fillet yield changes during starvation, in order to find solutions to optimize the production process. Spring and autumn were taken in the observed period, length, weight and fillet weight were taken from the parameters and condition factor and fillet yield were calculated. From the analysis of the obtained results we could not prove that Gilthead seabream is losing the weight throw the period of starvation, that should be manifested in reduction of condition factor. Comparing the results for autumn 2019 and spring 2020, it was determined that the fillet yield in autumn differs significantly in two criteria; starvation time and the class criterion. While in the spring there are no significant differences in the same comparison criteria. The reason for unexpected results is in the analysis of Gilthead seabream in class criterion, where condition factors between each other had differences in the way that bigger fishes had significantly higher condition factor. In that way it is hidden a decline of condition factor throw the starvation period. Regression analysis of the relationship between fillet yield and condition factor shows a very low correlation between these parameters, which leads to the conclusion that fish lose weight during starvation and fillets in proportion to the weight loss of the whole organism. Thus, the weight loss of the whole organism during starvation is also an indicator for the weight loss of the fillet as a final product.