Q. I have two veiltail goldfish, a black moor goldfish and a fantail goldfish. I was in the process of moving the fish to a larger aquarium. As I was pouring the water out of the smaller aquarium I noticed one fry floating in the sink, which, despite my efforts to save it, went down the drain. Is there any way to figure out which fish bred?
A. All sexually mature goldfish can “breed” in the sense that it takes both a male and female to produce fertilized eggs. No matter what form or name any “type” of goldfish is, it can breed with any other “type.” A male veiltail can breed with a female comet, a male lionhead gpldfish can breed with a female black moor goldfish, and so on. This is because all goldfish are really the same species: Carassius auratus auratus. The different types or varieties are physically different, but genetically compatible.
What you have discovered is that goldfish breed easily, and, if left to themselves, will mate without regard to differences in appearance (variety). Indiscriminant breeding among goldfish varieties eventually produces a “plain” ancestral goldfish that is brownish in color. These are often sold as feeder goldfish in pet stores.
Conversely, the beautiful varieties of goldfish are the result of intentional selective breeding among different types. By choosing the characteristics — color, finnage, body shape, size — we like and breeding successive generations, we can “fix” those traits. This type of genetic manipulation requires considerable amounts of time, skill and patience. This is why high quality show goldfish are so expensive.
If you want to play around with genetics you can create your own goldfish variety via selective breeding. Just figure out which fish are males and which are females and pair them up according to characteristics you like. Chances are that a few of the hundreds of offspring they produce will have some of the trait mixes you bred for.
Then take the offspring, raise them to maturity, and continue the selective breeding process. You may not produce a champion show goldfish, but you will certainly come to appreciate better the wonders of Mother Nature.