Severely emaciated fish show a common collection of pathologic changes in the muscle, liver, intestine, and ovary. The cause is one of many underlying known or unknown chronic diseases resulting in this overall presentation of cachexia, a complicated metabolic syndrome related to underlying illness and characterized by muscle mass loss and is often linked to anorexia.

Affected fish are very emaciated, and usually are notably lethargic.

The entire intestine shows atrophy and reduction in height of the plates, consistent with villar atrophy seen in mammals, and chronic inflammation of the lamina propria. The muscle often shows severe, diffuse myodegeneration. The liver exhibits severe reduction in the cytoplasm to nucleus ratio of essentially all hepatocytes, to the extent that at first appearance it is may be difficult to recognize as liver. With females, the ovary is atrophied and no large, vitellogenic eggs are present – i.e., only small, earlier stage oocytes are seen. Diagnosis. Severe emaciation (thinness) is a useful preliminary diagnosis. Confirmation is made by observation of the pathologic changes in histological sections.

Severe emaciation (thinness) is a useful preliminary diagnosis. Confirmation is made by observation of the pathologic changes in histological sections.