Culture characteristics of two species of piscine trypanosomes were compared. Trypanosoma catostomi from Catostomus commersoni was isolated in hypo-osmotic blood agar media but not in hyper-osmotic media. However, T. phaleri from Amia calva was isolated in both media. Only T. catostomi was stimulated to divide by diluting infected blood with water. The maximum number of T. phaleri and percentage of trypomastigotes were not affected by NaCl concentration. The maximum number of T. catostomi was inversely related to osmotic pressure and the percentage of trypomastigotes was directly related to osmotic pressure. This was confirmed by using equi-osmotic concentrations of NaCl, NaBr, Na acetate, KCl, choline-Cl or sucrose. Supplementation with urea had no effect on the number or morphology of trypanosomes. The survival of T. catostomi following cryopreservation was enhanced by prior incubation in hyper-osmotic media. Differential culture characteristics of these species may reflect adaptation to different host–vector systems.
