In 1984, he became employed in the ‘Laboratoire d’Ichtyologie Générale et Appliquée’ at the Muséum National d’Histoire Naturelle’, in Paris, France. As a specialist in African fishes he continued the work of the eminent Prof. Jacques Daget. During his years in Paris, he collaborated a lot with colleagues from the French ORSTOM (now IRD, Institut de Recherche pour le Développement), who were very active in West Africa.

In 1988, he returned to the Africa Museum to become curator of fishes, as a successor of two renowned ichthyologists on African fishes, Max Poll and Dirk Thys van den Audenaerde. In 1996, a second ichthyology position was opened, focussing on the cichlids of the great lakes, and Guy became responsible for research on and the collections of the non-cichlid fishes. While in Tervuren, he kept closely collaborating with his French colleagues, mainly in western Africa. His visited many countries in this region and launched or collaborated in projects in Ivory Coast, Cameroon, Congo Brazzaville, Gabon and Benin. He considered training as an important aspect of all his projects and many African ichthyologists in the region benefited considerably from his guidance. His research concentrated on taxonomy and biodiversity of African freshwater fishes, but through his projects and students he also got involved in aspects of aquaculture and fisheries. Catfish, and especially the clariids, remained his favourite group throughout his career. This led him also to collaborate in a project on the catfishes of South-East Asia.

He co-authored over 100 publications in peer-reviewed journals, almost a third of which as a first author, but mostly from his earlier periods. He wrote numerous other scientific notes and reports. He was one of the editors of the “Faune des poissons d’eaux douces et saumâtres de l’Afrique de l’Ouest” and the driving force behind the future publication of a similar book on the fishes of the Lower Guinea Province. In 1999, he became part-time lecturer at the Leuven University. Already early in its history, Guy became involved in FishBase, arranging the transfer of the collection data of the Africa Museum to the data encoding team in the Philippines. He was one of the founding members of the FishBase Consortium and coordinated the efforts of the Africa Museum on the entry and quality control of data of African fresh and brackish water fishes. He untimely passed away in his year as president of the Consortium.

About a year and a half before his death he started chemotherapy to treat a tumor. During his treatment he continued working and corresponding with his colleagues, mostly from home. One cannot but have a high regard for his dedication to African ichthyology and the amount of time and energy he put into his work.