When you change water in a tank, you should never change out 100% unless there is a drastic reason for this.
When doing a water change, you need to make sure that the temperature of the water being added back in is the same as the old water, and use the recommended dosage of water conditioner such as Prime or Amquel+
No, goldfish reproduce using external fertilization; goldfish are never pregnant.
You can use clean tap water for your goldfish, but not dirty or used water.
goldfish
using their gills they obtain oxygen from the top of the water.
It is not known. Roman baths were cleaned as needed. They were flushed by using the water supplied by the aqueducts.
bacteriophages.
After cleaning the carpet and painting the wall, we were exhausted.
That is actually Excriment. It is him using the toilet.
They are sitting over there on their blanket.
by sitting on it
There are several things that can cause a goldfish to sit at the bottom. One reason for this is if your goldfish has an internal bacterial infection;the outcome for this, if left untreated, is usually dropsy and eventually death. However there are several ways to affectively treat this: one way is to feed the fish a medicated food, the food should contain antibiotics, (most medicated foods sold at petstores do not contain antibiotics that are actually affective against bacterial infections, ) however one medicated food known to work well (and has three affective antibiotics) is "medi-gold"(goldfish medicated food). A second way to treat a bacterial infection is antibacterial injections, this method however should only be performed by a piscine vet. Goldfish may also sit at the bottom if they are suffering from an infestations of flukes(a microscopic flatworm). Almost all goldfish that are purchased have flukes and usually are immune to the parasite until their slime coat (immune system) is damaged or if they are stressed. An affective way to treat flukes is using one of the following: formalin,potassium permganate,Droncit, or fluketabs. Lastly one other cause for a goldfish to sit at the bottom would be if the goldfish has a deformed swimbladder; either the swimbladder did not form right or is full of water instead of air. Usually the only way to correct this is by consulting a piscine vet to surgically fix the swim bladder.
In theory, no. Goldfish are aquatic animals meaning they live in the water. They cannot be out of water for long periods of time without dieing due to lack of water. With that said, Goldfish cannot fly through air. If you threw a goldfish in air itd might be considered "flying" but in reality its most likely to die. Goldfish do not have the natural ability and talent to fly through air. If you built a tank that can support water and fish in the air and fly it then they can fly using that device, as we fly using a helicopter,jet,plane, etc.