My Thoughts on Culling

I realized after sharing a before and after culling photo on my Facebook page that a lot of people are very curious, and even a little confused, about culling goldfish. A few people even have some serious misconceptions about culling and goldfish breeding. I am by no means a geneticist or an expert long-time goldfish breeder, but allow me to try to clear some things up based upon my experience and what I have read from the experiences of many long-time goldfish breeders.

Culling is a fact of life for the serious goldfish breeder.

Culling is a fact of life for the serious goldfish breeder, and let me tell you why. The percentage of fry from any given spawn that will be worth keeping can vary greatly depending upon the parent fish. If the parent fish have been scrupulously line bred for many generations, a higher percentage of the fry will look like the parents. That’s what goldfish breeders aim for, and Japanese top view ranchu (TVR) are a pretty good example of this. But generally speaking, the majority of all fry from a single goldfish spawn will not be worth keeping. Goldfish genes “want” to revert back to their wild type (a brown single-tailed carp) over time because the qualities we prize so highly (telescope eyes, double tail, pearled scales, lack of dorsal fin, etc.) are all recessive genes. If you placed a few grand champion pearlscales into a pond and allowed them to breed without interference for many generations, you would end up with a pond full of brown single-tailed carp before too long. Goldfish are inbred; that’s how breeders can get them to appear the way they do. Breeders walk the fine line of making sure their fish are healthy and have a good quality of life while also meeting the variety’s standards. It’s not an easy task! Next time you meet a long-time goldfish breeder, please thank them for keeping these varieties alive for us to enjoy.

If you love goldfish; great! If you dislike culling; okay! That’s your opinion and I respect that. However, it’s not intellectually honest to love goldfish while simultaneously condemning culling. Do you know why? Because the goldfish as we know it could not possibly exist today without the very beneficial practice of culling. A single goldfish spawn can yield thousands of fry. Because we fish keepers do such a good job these days of caring for our fish and providing them with an ideal environment that’s completely free from predators or any other dangers, almost none of them will be killed off by “natural” means. (Just as an aside, even if they were allowed to be killed off by “natural” means, the ones that would have been killed off are the very ones that resemble their variety the best. Traits like telescope eyes, double tail, and pearled scales, make them less “fit” for their natural environment meaning they cannot compete with their siblings who have more wild type characteristics.) That means every single time your goldfish spawn (and goldfish can spawn every 5-7 days for many months on end depending upon the climate) you’ll have thousands of fish who will soon grow up to require a minimum of 10 gallons of space each. Even if you had unlimited space, money, and time to raise all those thousands of fish to adulthood, do you really think you could find quality homes for each and every single one of those fish (many of whom are severely deformed and cannot swim or eat properly)? And on top of that, could you maintain a line of fish that are relatively true-breeding so that we can still have the ryukin, oranda, and telescope goldfish varieties that we love so much? It would be an impossible task.

The goldfish as we know it could not possibly exist today without the very beneficial practice of culling.

Okay, so we now understand why breeders cull their fish. But what exactly do they do with the fish they have selected to be culled? There are a vast number of ways breeders deal with their culls. Some breeders euthanize the culls with clove oil, while others feed them to their adult fish. Yet others sell culls to their local pet store if the culled fry are a bit older. It just depends.
In the early stages, when the fry are only a few weeks old, breeders look for major deformities; most obviously severely crooked spines. These fry will not survive well in the future. Remember, the breeder is trying to maintain a line of fish that is healthy and viable. As the fry grow, the breeder begins to notice more deformities that are not quite as severe, but still limit the ability of the fish to thrive. Slightly bent spines, buoyancy issues, deformed mouths, etc. Something I read a long time ago on the Goldfish Keepers Forum that has since become my culling mantra is “a small flaw on a small fish will become a big flaw on a big fish”. Breeders look for these small flaws and try to weed out these fish as soon as possible so that the truly exceptional fish don’t suffer from overcrowding or the need to compete for resources. As the fry grow larger and begin to actually look like goldfish, more minor flaws will become apparent. Things like tripod tails, single anal fins, bumps on an otherwise smooth ranchu back, and other minor flaws disqualify the fish from being an exceptional example of its variety. Fish like this are sometimes referred to as “pet grade”. At this point, the breeder certainly has the option to sell the culls to their local pet store, as many do.

A small flaw on a small fish will become a big flaw on a big fish.

I hope I was able to shed some light on the subject of culling and perhaps help you see why it’s an integral part of goldfish breeding. Promoting awareness about all aspects of goldfish care is the focus of Solid Gold Aquatics. If you want to learn more about goldfish genetics or goldfish breeding I would refer you to the book “Goldfish Breeding and Genetics” by Joseph Smartt and also the Goldfish Keepers Forum for lots of good discussion by experienced long-time goldfish breeders. Thanks for reading and thank you for helping me grow the goldfish hobby.

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