Visualization of poikilocytosis as an emerging erythrocytic biomarker for fish health assessment

Fish health assessment is essential for maintaining sustainable aquatic ecosystems and ensuring the well-being of wild and farmed fish populations. Hematological parameters are crucial indicators of fish health, with poikilocytosis emerging as a fundamental marker with significant diagnostic value. Poikilocytosis refers to abnormally shaped erythrocytes in bloodstream, reflecting underlying physiological and pathological conditions. Poikilocytosis can occur in various fish species and can be influenced by environmental stressors, infectious agents, nutritional deficiencies, and exposure to pollutants. Morphological alterations in erythrocytes, such as acanthocytes, echinocytes, dacrocytes, schistocytes, spherocytes, and codocytes are common poikilocytes in fish. Understanding the relationship between poikilocytosis and fish health has important implications for disease diagnosis, monitoring, surveillance, and management. By quantifying poikilocytic changes, researchers and veterinarians can differentiate normal variations from pathological conditions, facilitating targeted interventions and treatment strategies. While most studies have focused on heavy metal toxicity, stressors, nutritional deficiencies, pollutants, and therapeutics, the etiological induction of poikilocytosis in fish health has been overlooked. Nonetheless, poikilocytosis remains a valuable biomarker for assessing fish health and their environment. This review highlights piscine poikilocytosis as a significant fish hematological biomarker and its importance in understanding their health and culture conditions.