Why do mosquito fish have black stripes under their eyes when they chase each other are mating or their tank is being cleaned?

Mosquito fish, or Gambusia affinis, display black stripes under their eyes as a form of visual signaling during social interactions, such as chasing, mating, or stressful situations like tank cleaning. These stripes can serve as a way to communicate aggression, stress, or readiness to mate, helping them establish dominance or attract partners. The stripes may enhance their visibility and convey important social cues in their environment. Overall, this coloration plays a key role in their behavior and social dynamics.