ABSTRACT. – We present a hypothesis of the history of the association of a clade of seven species of Aglaiogyrodactylus (a small clade of oviparous Gyrodactylidae), ectoparasites of loricariid catfishes. Ecological parameters (mainly abundance) of the associations were analyzed under a phylogenetic framework based on new and available data for hosts and parasites. Comprehensive sampling of fish and parasites was performed in a stretch of a stream on the coast of Paraná, Brazil (Marumbi River). Distribution of associations was not haphazard but no parasite species was collected only from a single host; correspondingly no ancestral-host reconstruction indicated the existence of a single host species for hypothetical parasite ancestor. Host range was strongly associated with ecological fitting and inheritance. The analysis could not identify any event of cospeciation but one event of historical oscillation in host range was revealed. Abundance was considered an adequate proxy for compatibility and suggest that cases of shift in this parasitological parameter are likely associated with divergence of the parasite following coadaptation to host species. One case of possible allopatric speciation was detected. The results are in accordance with the elements of the Stockholm Paradigm, which supports an alternative for studies of historical associations.