ABSTRACT

Background and Aim: Spotted scat (Scatophagus argus) is a euryhaline teleost of increasing importance in aquaculture, ornamental fisheries, and environmental monitoring across the Indo-Pacific region. Hematological evaluation is a valuable tool for assessing fish health, physiological status, and environmental quality; however, species-specific reference data for spotted scat remain scarce. This study aimed to characterize blood cell morphology and morphometry and establish preliminary hematological reference values for wild-caught spotted scat from Southern Thailand to support veterinary diagnostics, future research, and biomonitoring applications. 

Materials and Methods: Twenty-six wild-caught spotted scats were collected from Tha Sung Canal, Nakhon Si Thammarat Province, Thailand, between June and August 2025. Fish were anesthetized with clove oil before blood collection from the caudal vein into ethylenediaminetetraacetic acid tubes. Wright-stained blood smears were prepared for microscopic evaluation of blood cell morphology and morphometry. Hemoglobin (Hb) concentration was measured using an automated hematology analyzer, whereas packed cell volume (PCV), erythrocyte and leukocyte counts, differential leukocyte counts, thrombocyte counts, and erythrocyte indices were determined using standard manual hematological methods. Descriptive statistics were generated, and leukocyte morphometry was compared using the Kruskal-Wallis test followed by Dunn’s multiple-comparison test. 

Results: Four leukocyte types were identified: neutrophils, eosinophils, monocytes, and lymphocytes. Neutrophils and monocytes were the largest leukocytes and exhibited similar diameters (p > 0.05), although monocytes possessed a characteristically deeper blue cytoplasm that facilitated differentiation. Eosinophils occurred as small and large forms, whereas lymphocytes represented the predominant circulating leukocyte population. Juvenile male fish had a mean PCV of 0.24 ± 0.07 L/L, Hb concentration of 74.41 ± 20.94 g/L, erythrocyte count of 1.80 ± 0.68 × 10¹²/L, and leukocyte count of 32.47 ± 14.81 × 10⁹/L. Lymphocytes (16.14 ± 7.27 × 10⁹/L) were the predominant leukocyte subtype, followed by monocytes, neutrophils, and eosinophils.

Conclusion: This study provides the first comprehensive description of blood cell morphology together with preliminary hematological reference values for wild-caught spotted scat from Southern Thailand. These baseline data enhance diagnostic capacity for piscine hematology, support health assessment of ornamental and cultured fish, and provide a valuable foundation for future studies investigating environmental stress, disease, and the use of spotted scat as a bioindicator of freshwater, brackish, and mangrove ecosystems within the One Health framework.

Keywords: aquaculture, bioindicator, complete blood count, euryhaline fish, hematology, One Health, Scatophagus argus, Southern Thailand.