The impact of the 15-day consumption of enzymatic hydrolyzate of the mussels meat as a part of semi-synthetic diet on some stress biomarkers and apoptosis activity in various organs of growing male Wistar rats have been studied. Enzymatic hydrolyzate of the mussels meat (EMM) was obtained in pilot conditions using the enzyme preparation "Protozim". The animals of control group 1 (n = 8 with initial body weight of 179.4 ± 5.9 g) and experimental group 2 (n = 8, 176.3 ± 4.5 g) received a semi synthetic diet; the animals of the experimental group 3 (n = 8, 177.6 ± 4.0 g) received the same semi synthetic diet in which 50% of the casein was replaced by the peptides of EMM. On the penult day of the experiment animals of groups 2 and 3 were subjected to stress exposure by electric current on their paws (current 0.4 mA for 8 seconds) and were placed in metabolic cages for the collection of daily urine. At the 15th day of the study, all control and test animals were killed by decapitation under ether anesthesia and necropsied. The content of prostaglandin E2 and ß-endorphin in blood plasma was determined by ELISA test. The concentration of urine corticosterone was measured by HPLC. DNA damage and percentage of apoptotic cells (apoptotic index) were calculated in thymus by single-cell gel electrophoresis assay (Comet assay). The relative body weight increase of animals treated with EMM was significantly (p < 0.05) higher (68.2 ± 3.0%) than those in animals of groups 1 and 2 (57.2 ± 4.0 and 59.7 ± 2.8%, respectively). The apoptotic index in thymus cells of tested groups of animals (2 and 3) was significantly (p < 0.05) higher (1.13 ± 0.09 and 1.09 ± 0.01%) compared to intact animals of control group (1.04 ± 0.01%). Determination of ß-endorphin and prostaglandin E2 levels did not shown any significant differences between the groups. Significantly (p < 0.05) lower concentrations of corticosterone was found in the daily urine of stressed animals from group 3 (452 ± 78 ng/ml), treated with EMM, compared to stressed animals of group 2 that received a casein diet (834 ± 167 ng/ml). It has been shown that consumption of EMM with a high content of short and medium peptides has an impact on effectiveness of body weight gain of growing laboratory animals, and restrict the increase of corticosterone level in rats blood, which is typical for general adaptation syndrome.