Final answer:
The sword of a Broadbill Swordfish functions primarily as a defensive mechanism but cannot regrow to full length if broken. Bony fishes, including swordfish, have other sensory systems like a lateral line for detecting water vibrations.
Step-by-step explanation:
The main function of the sword in a Broadbill Swordfish is similar to the elongated snout seen in sawsharks, which is used for slashing and incapacitating the fish they eat. The sword acts as a weapon rather than as a sensory organ, a tool for digging, or an extension of upper lip bone. This leads to the conclusion that the correct function is primarily as a defensive mechanism, though it may also be used offensively in hunting. Furthermore, the lion's share of evidence suggests that once the sword of a Broadbill Swordfish is broken, it cannot regrow to its full length. Therefore, in the case of the damage to the sword, the answer would be 'No' to complete regrowth.
Bony fishes like the Broadbill Swordfish have osmoregulatory functions in their skin and possess a lateral line system for detecting vibrations, different from the electrosensitive pores seen in sawfishes, which are a type of cartilaginous fish. Sharks and rays, close relatives to sawfishes, have various adaptations such as abrasive skin for protection and well-developed sense organs for locating prey.