Objective: The objective of the research work was to observe pleomorphism (more than one morphological phenotypic expression of a species) in flagellate parasites (Trypanosoma and Trypanoplasma). Methods: The blood of selected vertebrate hosts (fishes, amphibians, reptiles and mammals) was scanned for haemoflagellate infectivity by examination of fresh blood (hanging drop preparations and haematocrit) and stained smears. The flagellate parasites (Trypanosoma and Trypanoplasma) were morpho-taxonomically identified and the phenotypic manifestation expressed as pleomorphism recorded for each species. Outcomes: Twenty-four species of trypanosomes from 12 fish hosts were discovered (12 species monomorphic, 6 each dimorphic and polymorphic). From amphibians and mammals, only monomorphic forms were encountered. The reptiles (Hemidactylus flaviviridis, Calotes versicolor) were not susceptible to trypanosome infection. Conclusions: Host-wise analysis indicated that Heteropneustes fossilis was most susceptible to trypanosomes. Trypanoplasms from fish too exhibited pleomorphism (6 species monomorphic, 2 each dimorphic and polymorphic).