Betta fish can't see in the dark. Betta fish are benthic fish, and their visual systems are not adapted to seeing objects in a completely dark environment. Although betta fish can live in dimly lit environments, they are unable to see objects when it is completely dark.
Betta fish have a certain degree of adaptability to light. They prefer dim and shaded environments, but not completely without light. A moderately dim and low-light environment is beneficial for betta fish to develop and maintain their vibrant colors and good physical condition. However, a completely dark environment is not conducive to their condition and coloration, and it may even affect their lifespan. Therefore, when keeping betta fish, it is necessary to provide moderate lighting instead of a completely dark environment.