There is a dearth of information on empirical studies on the impact of fish biodiversity on the welfare of farmers. Hence, it is important to investigate the role fish biodiversity, as a risk management measure, plays in the welfare status of aquaculture farmers in Ondo State, Nigeria. A multistage sampling procedure was employed in picking 192 respondents. Data were analyzed using the marginal treatment effects (MTE) approach to estimate treatment effect heterogeneity and policy-relevant treatment effects (PRTE) to simulate the effect of policy change. The empirical findings show that there is a huge heterogeneity in the gains from the adoption of fish biodiversity as a risk management measure concerning observed and unobserved factors. The results indicate that fish biodiversity adoption significantly increases revenue and reduces the poverty level of fish farming households at the reduced level of unobserved resistance to adoption. Also, PRTE results reveal that adoption rates of fish biodiversity could be significantly raised through the enhancement of fish biodiversity training and access to fish biodiversity information sources. Therefore, adoption of fish biodiversity as a risk management measure should be the priority of policymakers whose focus is on how to improve farm revenue and reduce poverty among aquaculture farmers.