The occurrence of Loma salmonae (Protozoa: Microspora) in farmed rainbow trout, Oncorhynchus mykiss Walbaum, in Scotland

A systemic infection of Loma salmonae is described from a farmed rainbow trout, Oncorhynchus mykiss Walbaum, population reared in fresh water in Scotland. Intact xenomas were associated with the blood vessels and pillar system of the gill lamellae and other organs. The secondary gill lamellae were hyperplastic with little evidence of fibrosis or inflammatory infiltrate. Uninucleate oval spores characteristic of L. salmonae are described. A low mortality was attributed to this outbreak which is believed to be the first occurrence in Scotland.