There are 46 species of poachers (Agonidae), and all of them have heavy body armor – protection against predators and aggressive conspecifics. But the protection of armor should come at a cost. We hypothesized that poachers pay for their armor in reduced maneuverability and increased body stiffness. To test our hypothesis, we recorded the natural flexibility of the Northern Spearnose Poacher (Agonopsis vulsa), by analyzing videos of its flight response, and found that the fish are quite flexible. We also used dead specimens in bending experiments to determine the body stiffness. The fish were bent in three different states (intact, with the plates removed, and with the muscle removed so that only the vertebral column remained) to quantify the contributions of each layer to whole body stiffness. To quantify the protection gained from the armor, we looked at the material properties (stiffness) of the plates. We used material testing to determine a stiffness parameter and compared it to vertebral bone from the same specimens. We found no difference in stiffness between plates and bones. While the plates do contribute to stiffness in the fish, the extent is not as pronounced as expected. In addition, they contribute much more heavily to the stiffness of the body region than the tail region.