Smith L., Gill M.E., 1988. High moralities in the perch, Perca fluviatilis L. associated with extensive granuloma formation. Acta Ichthyol. Piscat. 18 (1): 61-69.
Mass moralities were encountered in Perca fluviatilis from Axwell Park Pond in Northumberland. It was know from a previous study (Afi 1984) that this population has a high incidence of “liver cysts”. At the time of this morality fish had numerous “cysts” in and on the liver, the kidneys, spleen and heart and within the mesenteric tissues. Histological studies showed that these cysts were granulomas, with loci the nature of which could not be determined. At this time the infection was clearly of an epizootic nature, the high incidence approximately 60% falling to 2-3% after a population crash. Since the original description granulomas have been observed at two other locations in perch and dace. The cyclical nature of the infection, the unpolluted and widely separated habitats and the immunological nature of the response with secondary granulomas being produced suggest that the stimulus is biological in origin.