## 1 Introduction  
In constantly changing marine ecosystems, under conditions of increasing environmental and anthropogenic pressures, one of the greatest challenges for many organisms is coping with a variety of stressors, such as hypoxia, variations in pH, salinity and temperature, eutrophication, pollution, fishery and introduction of exotic species [1, 2, 3]. The response of an organism to a stressor is a dynamic process and the integrated result of two pathways: direct-acting, primarily through biochemical and metabolic processes, and indirect-acting, mainly through effects on the food chain, habitat availability and behavioural modifications of organisms [4]. To obtain information regarding the status of stressed ecosystems and their interaction with aquatic organisms, the use of biomarkers, especially in fish, has been recognised as a good approach [5]. In this context, fish haematological and biochemical parameters have become promising stress biomarkers and therefore helpful diagnostic tools [6; 7; 8; 9; 10; 11; 12; 13; 14]. In general, they are essential for assessing both fish health status and the extent of stress-related responses. Blood parameters are species-specific; they depend on biometrics, sex, age, maturity and nutritional status and therefore undergo many changes during the fish life cycle [14; 15]. All of this makes their evaluation difficult, so the prerequisite for the correct interpretation of blood parameters and their potential use as biomarkers is knowledge of reference values established on yearly cycles.  
There are several studies describing the haematological and biochemical parameters of the black scorpionfish, _Scorpaena porcus_[16; 17; 18; 19]. The activity of antioxidant blood enzymes was investigated in this species living in the Black Sea [18; 19]. In the nearby Dardanelles, blood chemistry (lipoproteins and enzymes) was analysed during the summer months [16], and variations in blood glucose were evaluated on a monthly basis for one year [17]. However, there is no comprehensive published information about reference ranges for blood parameters of presumed healthy black scorpionfish. On the other hand, this species plays an important ecological role in the Mediterranean hard-bottom and seagrass habitats and has a high value for ecosystem monitoring and management [2; 20; 21]. Therefore, the development of reference ranges is crucial for the health assessment of the black scorpionfish. This is exactly what has increased our interest in establishing annual cycle variations in numerous blood parameters of _S. porcus_. During the present study, fish were collected in the northernmost part of the Mediterranean, and haematological and biochemical parameters, including protein, lipid, carbohydrate and enzyme profile parameters, were analysed in detail. Specifically, this work provided reference values for 15 key health indicators, and their relationship with fish size was established. Moreover, measured blood parameters were correlated with different seasons and could serve as biomarkers of the influence of seasons on the local community of the investigated species. Once baseline values and seasonal variations are established, blood parameters can be monitored and can provide important information on the responses of the black scorpionfish to changing marine ecosystems.