I have a confession: I have been a goldfish torturer. A serial goldfish torturer, in fact. When my daughter was little, we thought it would be nice to have a little aquarium in her room, so we bought a 10 gallon aquarium and stocked it with 2 fancy goldfish from Walmart. Their names were Toby and Hobby. Toby or Hobby almost immediately perished and was replaced with another Toby or Hobby. I thought we were being amazingly benevolent fishkeepers to provide a whole 10 gallons of water for two fish, and a while later we added a pleco named Sucker to clean the algae. We had three fish, which, unbeknownst to me, were each capable of growing to eight inches (or actually much, much more in the case of the pleco), in a tiny aquarium with a cheap, small filter and no supplemental air because the air pump made too much noise. Against all odds, those fish lived for seven years, no doubt helped by the negligent aquarium maintenance schedule which probably made for a very good population of nitrifying bacteria (eventually).
My next goldfish mistreatment was when I created a tiny pond in a largish planter outdoors. That arrangement didn’t have any filtration at all, but there were a few plants. The goldfish didn’t survive very long, due to a raccoon massacre which also took out a couple of frogs that had taken up residence.
So this is the thing I didn’t know: goldfish get big and live a long time. Given good conditions, a single-tailed goldfish can grow to 12 inches and live 20 years. They’ll reach most of their full size in three years, but they grow as long as they live. I’m sure everyone has seen large goldfish in outdoor ponds, as I have, but I had also heard that they will only grow to fit the space available. Well, I was stupid and thinking wishfully to believe that. If they are in a small space, they will be stunted, both in growth and lifespan. Their internal organs become crowded and they die.
I read all kinds of advice on stocking rates from an aquaponics perspective, the most conservative of which was one pound of fish per 8 – 10 gallons of water. My system has a 100 gallon fish tank and a 50 gallon sump, but I use 120 gallons as a rough figure for total water since the water does not reach the top of either tank. I still haven’t figured out how much a full grown goldfish weighs, but I’m guessing it’s a pound more or less. According to these guidelines, my system would have 12-15 fish, though they wouldn’t “fill” the system until they were full grown in 3 years or so. My fish tank doesn’t hold all the system water, as I have a sump tank, so just to make sure everyone had enough space, I was leaning towards 12 (and I have mentioned 12 as the target population). One very popular aquaponics book has a chart showing the ultimate size of various fish varieties. It claims that goldfish reach four inches in three years, which would suggest that many more goldfish than 12 could successfully be kept.
I was curious about the weight and while I was googling on the subject, came across several sites dedicated to goldfish care. Other than mention of record setting goldfish, there was no mention about the ultimate weight of a goldfish there either, but there were recommendations for stocking them. The most conservative figure I came across was one goldfish per 55 gallons of water, in which case I could hold 2 adult fish in my setup. Other advice was to allow 40 gallons for the first fish and 12 for each additional one. Using those guidelines, I have water to hold almost 7 adult fish. My tank is four feet long, which is the minimum recommended for swimming room. I think where my system is better than most aquariums is in the huge amount of filtration in the form of the grow beds. They provide a massive amount of mechanical and biological filtration, better than even the largest aquarium models. I believe there is also a lot of oxygen in the water, due to the continuous water movement and airstones.
I’m comfortable with the eight youngsters I have in the tank now, and I think they will be fine to grow to their maximum size. Of course, I will be monitoring the water conditions, and if I am unable to keep the water in excellent condition, I am prepared to rehome some. Although I had thought that 12 would work, I’m now thinking that eight will do. It will take some time before the nutrient level of the water is optimum for plant growth, but these fish should grow reasonably rapidly over the next several months.
I do want the goldfish in my care to have good lives. There seems to be a tendency for aquapons to regard goldfish as throwaways because they are cheap. I see many examples of aquaponic people keeping five or six goldfish in a ten gallon aquarium. I expect an aquaponics system can hold slightly more than a typical aquarium, but I’m sure that keeping goldfish in conditions under which they struggle to stay alive does not make for a healthy system. Surely, it’s better to have the nutrients from a few, healthy mature individuals, rather than a bunch of sickly or stunted ones. I’m coming to see them as something more like chickens, those other creatures that no one gives any thought to, but who once you observe and interact with them, you see they are all individuals. I wasn’t really thinking when I started this project that I would be taking on eight more pets, and they mostly don’t have names, but I’m starting to be very protective of my little troubling (that’s the name for a group of goldfish).
Some people are starting to sell these mini aquaponics kits, that use goldfish bowls or three gallon betta tanks. Please do not buy one. There is no way for a goldfish to live a good life in a bowl like that. There may be filtration, but the surface area of the water is completely inadequate for oxygen, and there is no room for a fish to swim or grow. It will live a miserable stunted life and then die. It may take a few months, but a fancy goldfish should live for years. The betta tanks are little better, if minimally adequate for a betta fish, which can take oxygen from the air. The main problem with them is the lack of a heater, which condemns the poor betta to a chillier life than is optimum, given their tropical origins. Ideally, they would have at least five gallons of heated water to live in.