Abstract

In the United States, the number of households with pet fish continues to increase, and koi (Cyprinus carpio) are one of the most commonly owned pet fish.¹ In recent years, their popularity has increased along with the number of health-related issues associated with captivity.

Infectious and noninfectious diseases are frequently treated by extrapolating data from mammals and other fish species. Complete blood counts and biochemistry panels are routine diagnostics in the medical care of human and domestic animals but are less commonly used in fish medicine due to expense and lack of reference intervals. Published hematological reference intervals in koi are limited and either extrapolated from a review of common carp physiologic studies or based on small sample populations.^4,6,7 Additionally, reference interval studies in other fish species have shown differences in various parameters depending on age and sex of the animal.^2,3,5 The goal of this study was to follow standards by the American Society of Veterinary Clinical Pathologists to determine more robust normal hematologic and biochemical reference intervals for healthy koi stratified by age (juvenile vs. adult) and sex (male vs. female).

Blood was collected from 150 koi housed at a commercial ornamental finfish aquaculture facility (50 adult male, 50 adult female, and 50 juvenile). All fish had been previously screened for health and were negative for koi herpesvirus, carp edema virus, spring viremia of carp virus, and cyprinid herpesvirus 1. Juvenile fish were less than 2 years of age and adult fish were >5 years of age. Sex was determined in the adult fish via ultrasonography. Complete blood counts were performed on fresh whole blood, and biochemistry analysis was performed on fresh frozen plasma. Hematologic reference ranges were established for healthy koi for packed cell volume (PCV), red blood cell count, white blood cell count, and differential leukocyte counts. Plasma was analyzed for concentrations or activities of sodium, potassium, chloride, bicarbonate, phosphorus, calcium, blood urea nitrogen (BUN), total protein, aspartate transferase (AST), creatinine kinase (CK), gamma-glutamyl transferase (GGT), cholesterol, magnesium, and triglycerides. Values for potassium, calcium, triglycerides, cholesterol, and neutrophil count were lower in males, while AST, PCV, and lymphocyte count was higher in males than females. On average, PCV in all groups was higher than the previously reported value for PCV in koi, and potassium and cholesterol were lower than previously reported. These updated reference intervals, stratified by age and sex, will aid in accurate interpretation of bloodwork and contribute to improved diagnosis and management of fish morbidity.

Acknowledgements

The authors wish to thank the UC Davis Aquatic Animal Health Fellowship for supporting this project, and Anthony Quintero at Koi Enterprise for providing the fish for this study.

*Presenting author
+Student presenter

Literature Cited

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6.  Tripathi NK, Latimer KS, Lewis TL, Burnley VV. Biochemical reference intervals for koi (Cyprinus carpio). Comp Clin Pathol. 2003;12(3):160–165.