Neon glow fish, like all fish, require oxygen to survive. In the wild, fish obtain oxygen from the air that is dissolved in the water. However, in an aquarium, the water does not have as much dissolved oxygen as it does in the wild. This is because the water in an aquarium is stagnant and does not move around as much as it does in a river or lake.
An oxygen pump helps to add oxygen to the water in an aquarium. The pump does this by drawing air into the aquarium and then dispersing it throughout the water. This process helps to keep the water oxygenated so that the fish can breathe.
Without an oxygen pump, the neon glow fish would not be able to get enough oxygen to survive. The fish would eventually suffocate and die.