Final answer:
A malfunctioning lateral line in fish would impair their ability to detect vibrations, navigate, avoid obstacles, locate prey, and communicate, possibly leading to greater predation risk.
Step-by-step explanation:
If the lateral lines on a fish did not function properly, it would significantly affect a fish's ability to sense vibrations and movements in the water, which is critical for various behaviors. The lateral line system is a complex sense organ that runs along the length of the fish's body and helps them detect changes in water pressure and flows. This sensory system allows fish to navigate, avoid obstacles, locate prey, and communicate with each other. Additionally, without a functioning lateral line, fish could have difficulties maintaining their position in a school and might be more susceptible to predators.