It is not possible to counter a species. A species is a living thing that has been classified taxononomically. It can not be countered. It is also impossible to prevent something that has already happened. One can not prevent a species because it already is.
When goldfish are large enough, they are called carp. Tilapia is not a goldfish or a carp, although the species does have some similarity.
All goldfish types are the same species, so all types can breed.
No. They are entirely different species. Goldfish are a coldwater species of carp "Carassius auratus" and the Betta or Siamese fighter is a tropical anabantid "Betta splendens".
No a Goldfish is it's own species, while the Black Molly belongs to the Livebearer family (Guppies,Swordtails, Platys and Mollies
Goldfish need water to swim and breath in, not mud. There are some species of fish that have evolved to survive in mud but Goldfish are not one of those species.
Many other larger fish and many species of bird eat goldfish.
Rudd, Orfe, some species of Catfish will all be OK in cold water with Goldfish.
Any kind of goldfish will mix OK with any other kind of goldfish. Goldfish are all one species with many 'sports' that have been developed by selective breeding. The only No! No! is if you have some well bred fish and don't want them to cross breed at breeding time. Then you will need to keep type with type, otherwise, since they are the same species, they will cross breed and your resultant fry will be almost worthless crossbred goldfish.
goldfish are not always one color because they have different species. Also, goldfish can change colors over time. They won't always be gold or maybe they won't always be white or whatever color your goldfish is.
Rudd, Golden Orfe, Blue Dace, some species of Catfish. Check with your local pet shop what coldwater species they can get.
Yes they are different variations/varieties of the same species.
There is a kind of goldfish called the 'Shubunkin' with purple stripes on it but there is no pure purple goldfish species.