Hematological parameters of the European hake (Merluccius merluccius) in Toroneos Gulf, northern Greece: A case study

Abstract

Background: The European hake (Merluccius merluccius) is a commercially valuable demersal species widely distributed in the Mediterranean Sea. Assessing the condition of fish populations in their natural habitats is challenging due to the lack of reliable reference points. Objective: This study aimed to utilize hematological analysis as an economical method to evaluate the physiological and health status of European hake, addressing the gap in hematological data for this species. Methods: Blood samples were collected from the caudal vein of 40 adult European hakes caught from the Toroneos Gulf (northern Greece) using a commercial bottom otter trawl. An automated hematological analyzer was used to assess hematological parameters alongside biometric and biological indices. Results: Female hakes showed significantly higher white blood cell (WBC) counts, thrombocyte (TC) counts, and red cell distribution width (RDW) than their male counterparts. Strong correlations were observed among various hematological parameters, notably between WBC and red blood cells (RBCs), hematocrit (Ht), and hemoglobin (Hb); between RBC and both Ht and Hb; between TC and both mean platelet volume and platelet distribution width (PDW); and between mean corpuscular Hb concentration and RDW. Significant differences were noted in RBCs, Hb, and Ht compared to data from wild-caught European hake populations in Argentina and Denmark. Both trawling depth and duration were found to significantly affect RBC, WBC, Hb, and Ht values, while having no notable impact on TC. Fish captured at an average depth of 80 m and with a trawling duration of 30 min exhibited significantly elevated hematological indices. Conclusion: This study demonstrates that hematological analysis is a valuable, cost-effective tool for assessing the physiological and health status of European hake populations in the Mediterranean. Notable differences in hematological parameters based on sex, as well as significant correlations among key blood metrics, underscore the importance of understanding species-specific hematological profiles. The influence of trawling depth and duration on certain blood parameters highlights the need for standardized sampling protocols in population health assessments. These findings contribute essential baseline hematological data for European hake, facilitating more informed fisheries management and conservation strategies.