Growth of the fish parasite Ichthyophonus hoferi under food relevant conditions.
Physical and chemical parameters for growth of Ichthyophonus hoferi were studied to understand the ecology of this parasite both as a possible food contaminant and a fish pathogen. I. hoferi, formerly considered to be a fungus but recently shown to be a protozoan, can adapt to a wide range of environmental conditions and is a potent pathogen of several species of fresh and marine commercial fishes. The effect of temperature (0-30°C), pH (3-7) and NaCl (0-10% w/v) on growth were tested in vitro in a multi-factorial experiment. Growth was observed at all pH values, from 0 to 25°C and from 0 to 6% NaCl. No significant differences were detected in growth ability in the temperature range 0 to 25°C and from pH 3 to 7. However, increasing the concentration of NaCl significantly decreased the growth of I. hoferi and it is therefore unlikely that the parasite will develop and spoil processed products (pickled or salted herring) by continued growth. However, growth could be initiated by incubating spores under CO2 and this may be a potential problem in gas-packed fish products.