Shrimp muscle contains taste component compounds, such as glutamic acid and inosinic acid (IMP). When both are present, taste intensity increases by fourfold to eightfold compared to that when only glutamic acid is present. Inosinic acid is generated via adenosine triphosphate degradation in two metabolic pathways in which adenosine monophosphate (AMP) is generated and then degraded to either IMP or adenosine (AdR). We investigated post-mortem AMP degradation pathways in the shrimp Penaeus japonicus by measuring the activity of enzymes extracted from shrimp muscle and by isolating bacteria from shrimp muscle and examining their role in AMP degradation. The enzyme extract degraded AMP to IMP through high AMP deaminase activity, and in addition, we identified Shewanella sp. and Exiguobacterium sp. as mediating AMP degradation to AdR. Therefore, preventing an increase in bacterial numbers during storage is important for preventing AMP from degrading to AdR.