Bimonthly progress of a non-lethal infection by Glugea hertwigi in young-of-the-year smelt, Osmerus eperlanus mordax

Abstract

At regular intervals, during the summer of 1967, a total of 2923 smelts of age 0 were captured by means of the positive phototaxy shown by the young-of-the-year during night under artificial light.From June 22 to September 30, the Glugea hertwigi infection rate increased from 6.7 to 93.2%. The average number of Glugea cysts per specimen rose also from 0.08 to 57.44 during the same interval. The critical number of 250 Glugea cysts per specimen is not the only criteria of the lethal state of infection. Some young-of-the-year kept in captivity and having no apparent signs of Glugea infection enabled us to establish that Glugea cysts became apparent after 3 days of observation.