She is known for her work on the taxonomy of Digenea and was the first to describe the parasitic nematode Capillaria philippinensis, which causes intestinal capillariasis in humans.

[1] Velasquez continued her studies at the University of Michigan through a Barbour scholarship and was influenced by helminthologist George R. La Rue.

[1] Velasquez was hired as an assistant professor at the University of the Philippines Diliman in the Department of Zoology in 1966.

[3] One of Velasquez's interests was zoonotically important helminths; over 70 of her publications were dedicated to the life cycles and taxonomy of parasitic worms.

She conducted research into parasites of fish that are commonly used in Filipino cuisine, including the copepods that spend part of their life cycles in the intestines and gills of tilapia, giant trevally, maya-maya, milkfish, and the lobed river mullet.

In 1968, she described the parasitic nematode Capillaria philippinensis, which had been found in the intestines of a Filipino man from Ilocos Sur.

It was the first monograph dedicated to southeast Asian fish parasitology[1] and serves as a guide for aquaculture and fisheries management.