Hematological and Hematopoietic Analysis in Fish Toxicology—A Review

SIMPLE SUMMARY: Hematological analysis is one of the essential tools to assess the influence of organic and inorganic substances on fish. Thus, it is widely used in ecotoxicological and pharmacotoxicological studies. In this review, we demonstrate and discuss the use, strengths, and limitations of hematological as well as hematopoietic analysis in the context of fish toxicology. Since hematopoietic analysis can help to explain and understand the mechanisms of studied hematological changes, we highly recommend this method as a good complement to standard hematological tests. ABSTRACT: Hematological analysis is commonly used to assess the physiological state of fish. It includes red blood cell parameters, white blood cell parameters, and the number of thrombocytes per blood volume unit. Hematological analysis is one of the basic tools (often accompanied by biochemical and histopathological analyses) to assess the influence of organic and inorganic substances on fish. It is, therefore, applicable in both ecotoxicology and pharmacotoxicology. The advantages of this research method are the lack of need for specialized laboratory equipment and low costs, and the limitations are the need for extensive experience among the personnel performing the tests. One of the recommended methods of supplementing routinely determined hematological parameters is assessing the cellular composition and activity of hematopoietic tissue. As there is very little scientific data available on the issue of the effects of xenobiotics on the cellular structure of fish head kidney hematopoietic tissue, filling this gap should be considered an urgent need. Therefore, we recommend conducting research with the simultaneous use of hematological and hematopoietic analysis as reliable and complementary methods of assessing the impact of toxic substances on fish.