Nonisotopic detection of Loma salmonae (microspora) in rainbow trout (Oncorhynchus mykiss) gills by in situ hybridization

Loma salmonae, a microsporidian parasite of salmonids of the genus Oncorhyn chus, is a significant cause of economic loss in pen-reared chinook salmon (O. tschawytscha). Final stages of L. salmonae infections are easily recogn ized by the xenomas that form in the gills during sporogony. However, early prexenoma stages of infection (3 weeks or less after infection) are diffic ult to detect on histologic slides. An L. salmonae-specific single-stranded DNA probe labeled with digoxigenin was used to detect these prexenoma stag es of L. salmonae by in situ hybridization in experimentally infected rainb ow trout. This method allows detection of the parasite in the gills only 2 weeks after infection, providing a sensitive and specific way of detecting L. salmonae during the early stages of infection.