B. Spanggaard et al., GROWTH OF THE FISH-PATHOGENIC FUNGUS, ICHTHYOPHONUS-HOFERI, MEASURED BY CONDUCTIMETRY AND MICROSCOPY, Journal of fish diseases, 17(2), 1994, pp. 145-153
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.