No they do not; having gravel or not is really the choice of the fish keeper as far as how they want the tank to look. You can certainly leave it bare bottomed as many goldfish keepers do to give the fish more swimming room and easier time cleaning the debris from the bottom of the tank each week.
no
It is much better for the ifsh if you add a pump or filter in your tank.
No you don't need a tank to simply pump water from a lake. You would only need a tank if your using a pressure switch to turn the pump on and off.
HOPE THIS IS HELPFUL
Yes
no they need at least five gallons each. a thirty gallon tank is a good size tank to keep goldfish in.
You need a lot of things, unless you are raising goldfish in a bowl. You need: (for a tank) A filter A tank (not recommended under 5 gal.) Goldfish food Gravel Live or fake plants (underwater plants) Air pump (not required) Choice of decorations These can be very expensive sometimes, but it will keep your goldfish living longer and happier than in a bowl
Yes, goldfish are very messy. Goldfish need 10 gallons per fish, you actually need a 20 gallon tank or about a 70 liter tank for 2 goldfish. But the small tank will do while they are small, you will need to eventually get a larger tank.
While it isn't required that goldfish have an air pump in their tank. It can help your tank life by providing valuable oxygen to the fish. This isn't specific to just goldfish, as all aquatic life can benefit from the presence of a air pump. If you notice your fish swimming with their lips on top of the water level most likely they are trying to get air. This is especially true for tanks that have canister or over flow filters where the water is pumped and filtered without making contact with air.
Actually, I think that temperature is about right for your goldfish. But if you seriously need to, you need to change the temperature of the air around the tank. I suggest keeping it in a cooler room?
My Fantail Goldfish did that alot the first time I got him. I think it might be that they need to relax or they might be scared.
Yes, like all pet fish, goldfish need more oxygen than can be provided by just a bowl of water.
If you are coming from a city or county water main you do not need a water tank or pump system as the main should already be pressurized.