Further evidence for the presence of Renibacterium salmoninarum in salmonid eggs and for the failure of povidone‐iodine to reduce the intra‐ovum infection rate in water‐hardened eggs

Abstract

Unfertilized, water‐hardened eggs, obtained from a coho salmon, Oncor‐hynchus kisutch (Walbaum), with coelomic fluid containing large enough numbers of the kidney disease bacterium, Renibacterium salmoninarum, to make the fluid cloudy (∼4 × 10⁹ cells/ml), were examined by cultural and histological methods to determine (a) whether an earlier finding of the pathogen in coho eggs could be corroborated, and (b) whether iodine (500 mg/l, in the form of povidone‐iodine) was as effective at ridding them of the intra‐ovum pathogen as it was at freeing them of the extra‐ovum pathogen. The results confirmed that the pathogen does indeed occur within the egg (11–6%‐15‐l % of the eggs were infected in this manner), and suggested a location in the yolk for the pathogen. The findings also indicated that while iodine was very effective in killing the pathogen on the surface of the eggs it was completely ineffective in reducing the prevalence of the intra‐ovum infections. The results point out the need for a method for treating eggs internally and confirm the inadvisability of using eggs from salmonids with cloudy coelomic fluid.