Veterinary clinical pathology studies in fish can potentially provide a wealth of information for determining the health of fish populations. Environmental stress caused by poor water quality due to toxic gases, heavy metal toxicity, or pesticide toxicity may be detected at early stages by monitoring hematological, cytological and serum chemistry changes in fish. In addition, crowding stress, nutritional deficiencies, infectious and noninfectious diseases may be elucidated by analyzing fish blood and tissue samples.

A complete blood count including PCV, total protein, total RBC, hemoglobin, MCV, MCHC, MCH, total WBC and differential WBC may be readily analyzed in fish. Cytological techniques including, skin smear, gill clip, fin clip, abdominocentesis, impression smear, and fine needle aspirate allow for rapid evaluation of skin and gill pathology, parasitology, and bacterial infection.

Reliable comparative studies depend on good baseline data for each individual species using standard equipment and techniques. Automated blood counters and serum chemistry analyzers used in veterinary medicine work well for analyzing fish blood. Stains such as Wrights-Gemisa, Shaws, are excellent for analyzing fish leukocytes, and new methylene blue stain aids in cytological studies.

As the U.S. aquaculture industry continues to grow, studies in fish clinical pathology will play an increasingly important role in fish preventive medicine.