The article considers studying the physiological and biochemical parameters of the common sprat (Clupeonella delicatula caspia Svetovidov) taken in the western part of the Middle Caspian Sea at different periods of the annual cycle. There were studied the species in the pre-spawning state, at the beginning of spawning, at the feeding stage and at the pre-wintering stage. In fish muscle tissue the content of water-soluble protein and total lipids was determined. In the pre-spawning period, in male common sprat was recorded a positive correlation (p < 0.05) between the weight of fishes, fishing length and content of total lipids in muscles (r = +0.5206) and (r = +0.5039), respectively. In females no statistically significant dependence of the size-weight parameters and lipid content in muscles were recorded, which is probably due to the fact that lipids in their bodies were spent for energy needs, and to a greater extent than in males - for the generative function. In a comparative aspect, in the muscles of males and females no significant differences in the content of total lipids and water-soluble protein in the pre-spawning period were found. At the stage of the beginning of spawning, a decrease in total lipids and water-soluble protein was noted in the muscle tissue of the studied fishes, which is associated with an increase in energy consumption for sweeping out sexual products. During the feeding period the common sprat was characterized by an intensive accumulation of lipid reserves; the content of total lipids and water-soluble protein in the muscles increased with increasing length of individuals. In the pre-winter period stabilization of muscle lipid and increase in protein reserves were recorded, which is necessary for fish to ensure a normal existence in the subsequent stages of the annual cycle.