Growth of the fish-pathogenic fungus, Ichthyophonus hoferi, measured by conductimetry and microscopy.
The influence of pH and glucose on growth of I. hoferi was measured by indirect conductimetry and microscopy. Distinct resistance curves were produced using indirect conductimetry within 3 d at 15°C. Conductimetric changes were enhanced when the media were supplemented with glucose. Low pH (3-4) was required for continuous growth of the fungus, which was further facilitated by supplementation with glucose. At pH 7, growth occurred when the fungus had been pre-cultured at low pH and growth ceased after 3 successive transfers. Only vegetative stages of I. hoferi were observed; no conidia were present. At pH 7, growth was mainly observed as spherical bodies of varying size, with large numbers of nuclei and thick-walled spherical multinucleate bodies. Hyphal growth was abundant at low pH. It is concluded that the alternating pH simulated the natural conditions experienced by the fungus on transfer from stomach (low pH) to muscle (neutral pH) and reproducible sub-culturing was obtained when mimicking this pH cycle or when a low pH was maintained.