Can Hematology Be Used As A Diagnostic Tool In Fish Medicine?     Terry Hrubec   Department of Biomedical Sciences and Pathobiology; VA-MD Regional College of Veterinary Medicine; Virginia Tech; Blacksburg, VA 24061     Hematological techniques have been used with fishes for over a hundred years, yet the field of fish clinical pathology remains in its infancy.  Clinical pathologic tests are not used for diagnostics with fish, yet these tests are routine in mammalian and avian medicine.  Why is there this disparity?  Confusing and conflicting hematological data have been published, due to species and test methodology differences. There is also confusion and disagreement concerning maturational stages for specific cell lineages and for blood cell nomenclature.  Will fish health professionals ever be able to utilize clinical pathology as a diagnostic tool in fishes? Yes, as long as some basic guidelines are followed, i.e. reduce stress of capture, appropriate blood handling and sample preparation, appropriate analytical method. Databases of normal values must also be generated for each species.  Additionally, further information is needed to determine exactly how specific blood values are altered with disease.  Despite these apparent obstacles, I feel that clinical pathology will soon be a valuable diagnostic tool, particularly in detecting sub lethal conditions affecting production performance.