GROWTH OF THE FISH-PATHOGENIC FUNGUS, ICHTHYOPHONUS-HOFERI, MEASURED BY CONDUCTIMETRY AND MICROSCOPY

The influence of pH and glucose on growth of the fish pathogenic fungu s Ichthyophonus hoferi was measured by indirect conductimetry and micr oscopy. Using indirect conductimetry, distinct resistance curves were produced within 3 days at 15-degrees-C. Conductimetric changes were en hanced when the media were supplemented with glucose. Low pH (3-4) was essential to ensure continuous growth of the fungus, which could be f urther facilitated by supplementation with glucose. At pH 7, growth oc curred when the fungus had been pre-cultured at low pH. Growth of the fungus ceased after three successive transfers at pH 7 and this explai ns why earlier attempts to subculture have failed. Only vegetative sta ges of I. hoferi were observed; i.e. no conidia. At pH 7, growth was m ainly observed as spherical bodies of varying size, with large numbers of nuclei, and thick-walled spherical multinucleate bodies. Hyphal gr owth was abundant at low pH. The alternating pH simulates the natural conditions experienced by the fungus on transfer from the stomach (low pH) to the muscle (neutral pH) and reproducible sub-culturing is obta ined when mimicking this pH cycle or when a low pH is maintained.