In order to capitalize on zebrafish for exploring pathophysiology, a thorough understanding of its normal physiology is required. For example, the zebrafish is especially suitable for studies involving hematopoiesis (reviewed by Ward et al., 2002). The anatomical and morphological features of hematopoiesis are comparable to those in mammals (Amatruda et al., 1999). Zebrafish possess both erythroid and myeloid compartments, and there is strong conservation of hematopoietic gene expression, including transcription factors and signaling pathways (Conway et al., 1997; Liao et al., 1998; Oates et al., 1999). Large-scale genetic screens have resulted in the identification of hundreds of mutant phenotypes, including many with hematopoietic disorders (Weinstein et al., 1996). Several of these mutants present almost identical phenotypes to those of human hematopoietic diseases. For example, the sauternes mutant has anemia due to a defect in the erythroid S-animolevulinate synthase (ALAS2) gene, an enzyme involved in heme biosynthesis (Brownlie et al., 1998). Mutations in ALAS2 in humans cause congenital sideroblastic anemia, with many characteristics that resemble the sau phenotype. The sau mutant is the first animal model of this human disease. These mutants being recovered have tremendous potential for increasing our knowledge of normal hematopoietic processes as well as the pathophysiology of hematopoietic disorders. However, there is a serious lack of data describing the normal hematological characteristics of zebrafish. Normal hematological reference values for zebrafish are critical for interpreting results seen in mutant fish due to muta-genesis studies, transgenic applications, environmental stresses, or xenobiotic exposure.
Towards this goal, normal hematological and clinical chemistry parameters in adult zebrafish have been reported (Murtha et al., 2003b). Hematological values for zebrafish, including leukocyte differential counts and total erythrocyte counts, were within the ranges reported for mammalian species and fish. The predominant leukocyte seen in zebrafish was the lymphocyte, with smaller numbers of monocytes, neutrophils, eosinophils, and basophils. With the exception of increases in alanine transaminase (ALT), amylase, and phosphorus values, results of serum biochemical analysis were also within the normal ranges reported for mammalian species and fish. Serum biochemical studies of healthy fish are scarce, and results vary widely. Phosphorus values were only slightly higher than the upper range reported in some publications. ALT and amylase activities were most likely falsely increased due to some hemolysis in the samples. In summary, we believe these values will be useful in future studies that examine various disease models in zebrafish, normal aging of zebrafish, and screens of mutagenic zebrafish lines.
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