Abstract

Fish are stoic animals that are masters at masking their illness. While this evolutionary trait is a protective mechanism for these animals, it can make the job of the veterinarian working with them challenging. To determine the true immunologic status of a fish requires more invasive testing than an external examination. One of the first order diagnostics performed on fish is bloodwork. The complete blood count (CBC) is an important diagnostic for assessing the blood cell status of these animals. One potential pitfall associated with this diagnostic test is that counts must be done manually because all cell types are nucleated. The manual techniques used to assess CBCs in fish include methods that are as simple as reading cell numbers from a slide, to methods that are semi-quantitative and attempt to estimate cell numbers using standardized methods (e.g., hemocytometer). In an attempt to determine the value of these methods, blood samples were collected from 28 different cichlids. Manual slide counts were performed by two different evaluators and cytochemical stains (alkaline phosphatase, periodic acid Schiff) were performed to characterize the different cell types. Cytochemical stains reveal differences in staining characteristics for white blood cells within and between species. Agreement analysis was performed using Bland Altman plots and Passing-Bablok regression was performed to characterize bias. The level of agreement was found to vary from fair to good for cell count and cell types. It is important to recognize that CBCs in fish should be interpreted using a relative versus absolute scale.