This paper aims is to determine the welfare status of juvenile carp of different sizes and classes of the same age, by analyzing the main hematological parameters. The blood metabolic profile investigations provide valuable information regarding the physiological status of the cultured biomass. They can thus evaluate the hematologic response of juvenile carp reared under controlled conditions in a recirculating system, after being divided into four size classes (V1B1- Average body mass- 44,45 g/ex., V2B2-Average body mass- 63.85 g/ex., V3B3-Average body mass- 89.98 g/ex., V4B4-Average body mass- 141.5 g/ex.). The hemoglobin value, both at the beginning and end of the experiment, can be described as normal for this stage of development. The low hematocrit value (between 25 and 28 %) in the 4 experimental variants is possibly associated with an inadequate biochemical composition of the feed in terms of the presence of vitamins and some trace elements. The erythrocyte count values fall within the normal values for the species studied (1.10-2.20 mil/μl), with values that do not vary statistically (p>0.05) between the beginning and the end of the experiment for the 4 size categories. The erythrocyte constants HEM and CHEM recorded reduced values in the V3B3 growth variant at the initiation of the experiment while VEM recorded a higher value. In the other growth variants and at the two moments of the experiment (initial and final), the values of the three erythrocyte constants fall within the range of normal values for the species studied. The general conclusion resulting from the analysis of the main hematological indicators showed that the physiological state of health of the carp was not significantly influenced by the size class. After correlating the blood metabolic profile quantitatively with the indicators of technological performance, we can say that the crop biomass gains were higher in the case of larger than in the case of smaller specimens.