In this article, an analysis of six fisheries biology assignments involving mathematical models is conducted, focusing on the type of participation that they offer. The purpose of the analysis is to identify the characteristics of the mathematical discourse of the assignments and to expose their relationship with the biological context with the purpose of understanding the role of mathematics discourse in other academic discourses. The theoretical orientation of the study is informed by commognitive theory which views learning of an academic discourse as the process of becoming a participant in that discourse. Data analysis revealed various aspects of mathematics wordings, tools and routines essential in the expected solution trajectories of the assignments and two types of required transitions, intrinsic and extrinsic, between mathematics and biology narratives. The article offers analytical and theoretical explanations for why this is the case as well as directions for future research.