Anything which breaks the water surface will help with aerating and circulating the water. If it is moving the water causing surface agitation then yes it is providing aeration. Like stated, anything agitating the surface, whether it is the wind, a filter, or throwing pellets in the water, will provide some oxygen.

Too much oxygen in water can lead to the potentially lethal gas bubble disease, in which gas comes out of solution inside the fish, creating bubbles in its skin and around its eyes. (Excess nitrogen, however, is a far more common cause of this disease.)

The most telling sign that your fish need more oxygen is if you see them gasping at the surface — they will also tend to hang out back by the filter output. This area of your tank tends to possess the highest oxygen concentration as it is near the most disturbed surface.

Air Pumps. An air pump simply bubbles air through your tank. Air pumps serve two purposes. First, they insure that your tank maintains an adequate concentration of oxygen.

In case of emergency, you can instantly increase the oxygen level in your aquarium by simply pouring down some aquarium water using a jar from some height. You can also do a large water change of up to 50% of water to increase oxygen in the fish tank.

Fish can survive about two days without an air pump in completely still water. However, with the right kind of filter producing lots of surface water movement, an air stone may not be required at all.

Below are a few types of fish that are best suited to living in a large bowl:

1. Betta fish (Use a heater)
2. Guppies.
3. White Cloud Minnows.
4. Blind Cave Tetras.
5. Salt and Pepper Corydoras.
6. Zebra Danios. To get a few more ideas for smaller bowls that are 2.5 gallons or less.
7. Ember Tetra.
8. Pea Pufferfish.

Livebearers are famous for being stress free and easy to care for. This group includes not only Platies but their close cousins the Swordtail, Guppy, and Molly. Each has their charms but I find Platies to be tied with Guppies for being the most low maintenance fish around.

about 7 to 9 hours

Quickly changing large quantities of the water will disrupt that chemistry and shock fish, causing death. The salinity of the water (for saltwater aquariums), pH levels, filtration efficiency, and other quality issues must be maintained within ideal levels, or any one of them could be responsible for dead fish.

Originally Answered: Does flushing a fish down the toilet kill it? Uh, yes. The pipe underground of the toilet does not drain directly to the ocean. The water you flush goes to a sewage treatment plant where physical things like toilet paper is taken out (the fish would die there if not in the pipes).

Some relatively humane slaughter methods have been developed, including percussive and electric stunning. However, most fish harvesting continues to use methods like suffocation in air, carbon-dioxide stunning, or ice chilling that may not optimise fish welfare in some instances.