Willem has been a member of the Dutch cichlid association (NVC) for almost 30 years and currently serves as their President.
About 15 years ago he started collecting cichlids in México and other countries in Central America. Most of these trips he made together with Ad Konings and some with Juan Miguel Artigas and Don Danko. On the first trips he focussed on collecting cichlids but on later ones Willem tried his hand at shooting video both above and below the waterlevel. This has resulted in both bringing (new) fish into the Dutch hobby and a number of films.
The last three trips he made had Nicaragua as destination. He visited most of the crater lakes in that beautiful country searching for cichlids, concentrating on Laguna Xiloá where he put his divers license to good use being able to get video footage from depths of 20 meters or more. He ended up with a practically complete collection of cichlids from Laguna Xiloá (over 10 species) now residing in the Cichlidarium. One tank features a group of 7 Amphilophus amarillo (13") and 5 Parachromis dovii of about the same size. Central American cichlids can indeed be kept in groups!
- Central America: an overview of the (geologic) history of Central America and the origin of the cichlids now occurring in that area.
- Cichlasoma: the systematic history of that once large cichlid genus and a presentation of the species related to Cichlasoma (both South and Central American).
- Breeding Central American cichlids at home: examples of the breeding of many Central American cichlids in the home aquarium.
- Nicaragua: cichlids from the crater: a travelreport form Nicaragua showing many of the species in their natural habitat (also available as a film).