SUMMARYThe aquatic hyphomycetePleuropedium tricladioidesis reported for the first time from the freshwater nematodeNeomesomermis flumenalis.The optimum temperature for growth of the fungus was 20 C. Concentrations of phosphate in the range of 2.5 to 90 mM were equivalent in their growth yield, and the optimumpH range for growth was 4.75 to 5.75. Concentrations of vitamin-free casamino acids under the conditions used were limiting at 2 g/liter and lower; 4, 6, 8 and 10 g/liter produced the maximum mycelial yields. Glucose utilization was not detected until da 6 of incubation; however, by the time the peak of the growth curve had been reached (da 13) 92% of the glucose had been utilized. The utilization of ninhydrin-positive substances from media containing casamino acids with and without glucose was determined. The compounds L-serine, L-alanine, L-methionine, L-leucine, L-phenylalanine and L-arginine were utilized both in the presence and absence of glucose. Ammonia was utilized in the presence of glucose and produced in its absence. L-glutamine and/or L-asparagine and DL-cystathionine were released into the medium only in the presence of glucose. The polyamines putrescine, cadaverine and spermine were not detected in either medium during the 18-da incubation period. Spermidine was detected in trace amounts in the medium initially containing glucose on da 16, 17 and 18.