This work could not have taken its present form without the support of my parents, my wife Becke, and my family and friends.

I would like to thank Professor Kurt J. Peters for setting up the contact and giving guidance in the entire process of planning and implementing the research. Professor Jens U. Nagel contributed with comments and suggestions on the methodological side of this work. Professor Carsten Schulz proved an invaluable and critical discussion partner concerning biological characteristics.

The study was conducted with the help and support of the WorldFish Center, Penang, Malaysia. Special thanks are owed to Dr. Johann Bell and Dr. Ahmed Mahfuzuddin who gave assistance and advice in this project. My appreciation also goes to Mr. Blake Ratner, Mr. Mark Prein and other staff from the WorldFish Center for suggestions, comments and assisting in the work.

Assistance from the Ministry of Fisheries, Research Institute for Aquaculture No. 3 in Nha Trang, Vietnam, proved invaluable. Especially Mrs. Nguyen Thi Xuan Thu was of great help through her interest, suggestions and help in providing the legal documents to accomplish my field studies.

Further support came from the Department of Aquaculture of the University of Fisheries in Nha Trang, Vietnam. I would like to thank Mr. Hoang Tuong and especially Ms. Hoa for many valuable discussions and help in the adjustment of participatory methods to cultural and social circumstances.

I want to express my gratitude to the following persons that helped translating, providing transport and simply spending time with me: Mr. Nguyen Tan Lo and Mr. Huy for translation, Ms. Nguyen Tran Hoang Phuong and Ms. Hien for Vietnamese lessons and her sister Ms. Duyen Thu Hong for setting up all the contacts.

For help and inspiration during the preparation of this study I would like to thank Becke, my friend Mr. Jes Weigelt for many valuable discussions and especially my mother Mrs. Karin Strehlow for reviewing the draft.

This work could not come into existence without the funding from the Advisory Service on Agricultural Research for Development (BEAF), in this respect I would like to thank Mrs. Marlene Diekmann.