Although fish farming in Cameroon started in the late 1940s, currently the country meets only half of its domestic demand for fish. This article examines the complex issue of farmers' adoption decisions and attempts to answer why there is a lag in the diffusion process. The theory of behaviour modification and key variables of adoption form the conceptual framework of this study. The paper makes use of primary data obtained through semi-structured interviews, key informants and focus group discussion. This paper reveals that inputs provided by public or non-governmental bodies, favourable environmental conditions and socio-cultural attitudes act together as driving factors towards fish farming adoption. Little administrative presence and a low local effective demand for fish have a negative effect on the adoption process. Characteristics like trialability, relative advantage and complexity of the innovation exert a significant hindrance on farmers' adoption behaviour, while compatibility and observability provide a certain explanation. The findings clearly support the observation that fish farming is an attractive activity for medium-scale farmers most of whom are able to: run several ponds, and manage feeding, maintenance, storage, transportation and marketing effectively. With regard to small-scale farmers, staple food cropping is seen to have a comparative advantage over fish farming. This study fills gaps in existing knowledge of fish pond aquaculture diffusion in Cameroon. To realize a positive impact on the adoption decision process of this activity, this article suggests donors focus on medium-scale farmers, on improving organizational structures of farmers, and on strengthening the fragile extension system and the research on fingerlings production. (Contains 2 figures and 3 tables.)