Mediterranean scallop (Pecten jacobaeus, L.) is the endemic bivalve of the Mediterranean. It naturally occurs in larger quantities only in the Northern Adriatic. In the Northwestern Istria, Mediterranean scallop is a relatively common finding, fished for commercial purposes. Overfishing of the species may occur because of a small fishing area and high market value. Knowledge of the physiological status of the Mediterranean scallop through analyzing the biochemical, lipid and fatty acid structure of tissues as well as histological status during the seasons is important for its preservation in the natural environment and possible aquaculture. The aim of the research was to examine the seasonal impact in both sexes and four tissues (gills, digestive gland, gonads, muscle) on biochemical indicators (concentration of metabolites, proteins/enzymes, electrolytes, antioxidant capacity, status of lipids and fatty acids (saturated, monounsaturated, polyunsaturated, omega-3 and omega-6 fatty acids)) and histological-morphological characteristics. Shellfish were collected seasonally (spring, summer, autumn and winter) by a bottom trawl three nautical miles off the Western Istria coast. The seabed of covered area was predominantly sandy with maximum depth of 40 meters. Upon hauling, the catch was emptied on the deck, scallops were separated from the rest of the catch, sorted, counted and transported on ice to the coast. There they were inspected for external signs of mechanical damage, wet weighed and measured (total mass of the shellfish, mass of soft tissue, mass of individual organs, length and width of the shell). Based on the measured data, the length-weigth ratio, condition index (IK) and gonadosomatic index (GSI) were calculated. The samples determined for the measurement of biochemical indicators, lipid and fatty acid status were placed in polyethylene bags with sealing strips. After that, the samples were frozen and kept at -86 ˚C. Samples for histological-morphological analyzes were not frozen, but stored in a 4% formalin solution. Hydrographic parameters (sea temperature, salinity and dissolved oxygen) were measured during seasons. Four scallop tissues were studied for the selected biochemical properties, antioxidant defenses and free radical scavengers. These included tissue magnesium (Mg), calcium (Ca), glucose (GLU), triglyceride (TRIG), and cholesterol (CHOL) concentrations, activities of lactate dehydrogenase (LDH), superoxide dismutase (SOD), glutathione peroxidase (GPx), total antioxidant status (TAS), malondialdehyde (MDA), total carotenoid and astaxanthin contents. Total lipids and fatty acids were analyzed in the digestive gland, muscle and gonads. Fatty acids were grouped according to their degree of saturation, as saturated (SFA), monounsaturated (MUFA), and polyunsaturated (PUFA) fatty acids, and as omega-3 (n-3), omega-6 (n-6), and omega-9 (n-9) fatty acids. The research results indicate that environmental conditions (sea temperature) and the reproductive period are the main processes that influence the seasonal patterns of biochemical and fatty acid parameters of the Mediterranean scallop. Seasonal variation of developmental stages and an extended reproductive cycle showed strong gametogenic and reproductive activity in autumn (gamete maturation) and winter (spawning), with intensification of the gametogenic stage in warm months, when reproductive activity is at maximum, as well as summer spawning. The significant role of energy metabolites and lipids in the resistance of Mediterranean scallops to stress caused by temperature extremes was proven. A decrease in antioxidant defense was observed during the cold months, along with the accumulation of lipid peroxidation products in tissues. The carotenoid astaxanthin was the most abundant in the winter months. Given that carotenoids were most numerous in the tissue of the digestive gland, it is most likely that they were ingested through diet. As the energy reserves stored in the muscle are used for gamete development and vary with respect to the availability of food, it is possible to conclude that the catabolism of the muscle reserves did not take place due to the availability of food which was sufficient for both somatogenic and gametogenic growth of scallops. The fatty acid composition of Mediterranean scallop differed between tissues and seasons and indicates that muscle, which is the reason for commercial exploitation of the species, is best for consumption in spring and summer, because the sum of unsaturated fatty acids (MUFA and PUFA) was greater than 50% in total lipids. The n-3/n-6 fatty acid ratios were the highest in that period, while cholesterol and glucose values were the lowest.