What must a fishing vessel display at night when it is at anchor?

A fishing vessel at anchor is required to display specific lights to ensure that it is visible to other vessels during nighttime. According to the International Regulations for Preventing Collisions at Sea (COLREGS), a fishing vessel at anchor must exhibit two lights: one red and one white, positioned vertically. The red light is displayed over the white light, indicating that the vessel is engaged in fishing operations while at anchor.

This configuration is essential for both safety and navigational purposes, as it alerts other vessels to the nature of the fishing vessel's operation, thereby helping to prevent collisions. The combination of lights specifically denotes that the vessel is not just at anchor, but specifically involved in fishing.

Other options would not accurately convey the status of the vessel or comply with regulations governing nighttime visibility for fishing vessels at anchor, thus they do not meet the requirement.