The self-recruiting species (SRS) are aquatic animals that can be harvested regularly from a farmer managed system without regular stocking as described by Little (2002a, b). The potential and current role of self-recruiting species from farmer managed aquatic systems (FMAS) is often overlooked, whilst much attention has been given to stocked species (often associated in conventional culture ponds and cages) as well as the fisheries sector (often relates to large water bodies i.e. river lakes and reservoirs). Using the combination of qualitative and quantitative research approaches, the current status, the important contribution of SRS and factors undermining this contribution to the livelihoods of rural households in mainland Southeast (SE) Asia were investigated. The overall analysis of this research was done based from the sustainable livelihood (SL) framework (Scoones, 1998; DFID, 1999) in order to have a broader understanding of the importance of SRS as well as the rural livelihoods in selected areas of mainland SE Asia which often benefit from this resource. The research was carried out in rural villages of southeast Cambodia (SEC), northeast Thailand (NET) and Red River Delta in northern Vietnam (RRD). The sites (region of the country) were selected based from the intensity of aquaculture practices (less established and mainly relying on natural production, aquaculture established but also relying on natural production and mainly aquaculture dependent) as well as the agriculture i.e. intensiveness of rice production. Eighteen villages (6 villages/ country) were selected to represent the two agro-ecological zones (i.e. LOW and DRY areas) of the study sites. In order to fully assess the situation and meet the objectives of the research, the study was carried out using three stages which dealt with different approaches and sets of participants/respondents; i) participatory community appraisal (PCA), ii) baseline survey and iii) longitudinal study. The different stages of the research were carried out during the period of April 2001 until September 2004. During the first stage, a series of community appraisals using participatory methods were conducted in all of the participating villages in the three study sites. The participatory appraisal was conducted in order to understand the general rural context in the villages as well as the importance of aquatic resources. Moreover, the PCA in a way helped build rapport between the researcher and the communities. The series of appraisals were conducted with different wellbeing and gender groups (better-off men, better-off women, poor men and poor women). The various shocks, trends and seasonality that influenced the status of living in the community, diversified livelihoods and the differences in preference of socioeconomic and gender groups were analysed in this stage. The important aquatic animals (AA) and the local criteria for determing their importance were the highlights of this stage of the research. The important AA identified were composed of large fish (Channa spp., Clarias spp., Hemibagrus sp, Common, Indian, Silver and Grass carps), small fish (Anabas testudineus, Rasbora spp., Mystus spp., Carassius auratus) as well as non-fish (Macrobrachium spp., Rana spp., Somanniathelpusa sp., Sinotaia spp.) which were particularly important to poorer groups in the community. The local criteria used were mainly food and nutrition related (good taste, easy to cook, versatility in preparation), abundance (availability, ease of catching) as well as economic value (good price). Significant differences were found between various interactions of sites, agro-ecological zones, gender and wellbeing groups. The second stage of the research was the baseline survey (cross-sectional survey) which was also carried out in the same communities and collected information from a total of 540 respondents (30 respondents per village or 180 per country). This stage of the study was carried out in order to generate household level information (mostly quantitative) regarding the socio-economic indicators to triangulate the information generated during the participatory appraisal and the different aquatic systems that existed in the community as well as the various management practices used (not limited to stocking hatchery seed and feeding). The different livelihood resources (human, physical, financial, natural and social capital) and the diversified strategies of rural households in SE Asia were analysed in this phase. Another highlight of this phase was the understanding of the various aquatic systems that rural farmers managed and how they related to the existence of self-recruiting species. The common aquatic resources identified during this phase included farmer managed aquatic systems (FMAS) and openwater bodies (OWB) where rural households usually obtained their aquatic products. The various types of FMAS which included ricefields, trap ponds, household ponds, culture ponds and ditches were identified as important aquatic resources which mainly provide food as well as additional income to the rural poor. All of these FMAS were being managed at various levels which directly affected the SRS population. Different types of farmers were identified based on their attitudes towards and management of SRS: i) SRS positive, farmers who allow and attract SRS into the system, ii) SRS negative, farmers who prevent or eliminate SRS and iii) SRS neutral, farmers doing nothing that would encourage or prevent SRS from entering into the system. Variations were related to the main factors (i.e sites, agroecological zones, wellbeing groups) and their interactions. The final stage of this study was the year-long household survey (longitudinal study) that investigated the seasonality of various aspects of rural livelihoods, status of the different aquatic systems and the important contribution of AA in general, and SRS in particular, to the overall livelihood strategies employed by rural farmers. This phase involved a total of 162 households (9 per village or 54 per country) selected based on the aquatic systems they managed and had access to. Other socio-economic factors (gender and wellbeing) were also considered during the selection of participants in this phase of the study. The results of the year long household survey highlighted the important contributions of SRS: i) to the total AA collections which were utilised in various ways, ii) contribution to overall food consumption in general and AA consumption in particular (which was found to be the most important contribution of SRS), iii) contribution to household nutrition (as a major source of animal protein and essential micro nutrients in rural areas), iv) contribution to income and expenditures, and v) improving the social capital of rural households (through sharing of production and mobilizing community in local resources user group management). Moreover, the social context and the dynamics of inter and intra household relationships were understood, especially the gender issues on division of labour (where women and children played an important part on the production), access and benefits (how women and children were being marginalised in terms of making decision and controlling benefits). The various results of the combined approaches that were utilised in all stages of the research were analysed and presented in this thesis. The results of the community appraisals and the baseline survey were used in setting the context (background) of each topic (e.g. livelihood activities, AA importance, etc). Meanwhile, the results of the longitudinal survey were used in illustrating the trends and highlighted the seasonality of particular issues. Overall the study contributed to knowledge by elucidating the status and roles of self-recruiting species in maintaining/ improving the overall livelihoods of rural farmers in Southeast Asia.