Fish swimming with mouth always touching the water surface

Fish swimming with their mouth constantly glued to water surface is a sign that they are gasping for breath. However, the reason for them being short for breath usually isn't the low oxygen concentration in the water itself, but toxic effect of water pollutants: ammonia (NH₃), which burns their gills and disables the fish from extracting oxygen from the water; and nitrite (NO₂^-), which binds to hemoglobin in fish's blood and blocks oxygen from being transported to all the tissue.

Nitrite poisoning could be recognized by looking at the color of fish's gills - healthy gills are bright red, while nitrite poisoning makes them tan-brown.

If the bowl has diameter of around 1 foot, then - considering its shape visible on the photo - it has the volume of less than 10 liters and this is extremely small. In case of goldfish, there should optimally be at least 20 gallons (around 76 liters) of water volume for one goldfish and 10 gallon (around 38 liters) for each additional beyond one. Goldfish are exceptionally dirty and have a high bio-load, which means they require a large amount of water to safely dilute their excreted waste before it gets neutralized by the filtration system.

Having a functional filter in the aquarium is essential, so please install it as soon and possible.

Please also read about nitrogen cycle in the aquarium - it takes around a month to cultivate the essential bacterial flora in the filter to enable it to safely neutralize the waste generated by animals and decomposing matter in the aquarium.

Also, holding water overnight doesn't necessarily make it appropriate for aquarium use because some tap water facilities sanitize it with chloramine instead of chlorine. Chloramine is synthesized in water by treating it with both ammonia and chlorine. Chloramine isn't volatile enough to diffuse out into the air as fast as chlorine and it could take well over a week for it to do so. It is a lot safer and more convenient to use a water conditioner from pet shop - it doesn't need to be a fancy nor expensive one, just please make sure it says "neutralizes chlorine and chloramine" on the label. Both chlorine and chloramine could also burn fish's gills and cause them to gasp for breath on the water surface.