Koi vs Goldfish

[georgia washington]

I want to use koi or goldfish in my aquaponics system.  I have narrowed my selection to these two fish because they can withstand a wider temperature range (neccessary in Missouri climate) and mostly because they are known to produce a larger quantity of waste (ammonia).  The more ammonia, the more nitrates (provided sufficient bio-filter capacity) which should allow for more plants.  I want to maxamize my limited fish tank capacity by choosing the right fish that will produce the most waste/ammonia.  It's my understandng that I can stock more goldfish per volume of water than koi.  Is this correct?  And if so, wouldn't that mean goldfish would be the better choice for producing more waste/ammonia/nitrates in a given volume of water...than koi?  I guess this is just a question of fish density comparison.  But perhaps I'm overlooking something.  Any thoughts would be appreciated. 

[TCLynx]

Koi grow bigger which is why you need more water per fish.  Bigger fish smaller fish, it is the overall total weight of fish that kinda dictates how much they eat and how much they poop for you.

[Carey Ma]

I'd go with goldfish esp if you don't plan on eating or selling. You can pack more small fish in a tank than the larger koi but need a good robust filter and more oxygen. And if something goes wrong, it's cheaper to replace.

[Kirk Ellern]

Basically same thing.  You'll compare the weight of fish to the amount of water in your system.  Koi are bigger, obviously.  Koi CAN get up to 30 lbs, I'm told.  If you have a lot of space in your fish tank they are much more fun to show friends and neighbors than gold fish are.

 

Both Koi and Goldfish give of an enzyme.  When that enzyme gets to a certain level in the water they will stop growing. 

 

Problem: You will have a lot of water in your grow beds in addition to the fish tank.  This could give the fish the chemical illusion that they have a lot more grow space than they do.  Your Koi could end up WAY too big for the tank and then, since they like to swim in circles, they grow up deformed and stunted and that's not cool.  My Fish Tank is only 55 gallons (but I'm upgrading to 100 this weekend)

 

Solution: Shubunkin Gold Fish.  (http://en.wikipedia.org/wiki/Shubunkin) They look like Koi but they only grow to about 12 inches tops.  They eat at the top so when people come over they come up and show off a little.  The 2 gold fish I have in there from initial cycling stay hidden and boring.  I think the name Subunkin is roughly translated as "Too cheap for Koi". I got 3 at a local garden shop that has fish for ponds for about $5 each. 

 

My theory is that they will grow as my plants grow and this has proven correct.  The Nitrate levels have been about just right for my system.  If I want more Nitrogen I feed them more (its possible that uneaten food is increasing my Nitrogen, of course).  Too much; feed them less OR (this is my trick for a super green lawn) take some of the water from the fish tank and pour it on the rest of the lawn/garden for a little fertilizer.  Just make sure you replace that bucket or two a day with dechlorinated water.

[Dale Parker]

Koi Fish is good for outdoor gardens for its large size and attractive colors and it is becoming a popular choice for koi aquaponics systems. Whereas the most used aquaponics fish. Koi can live in temperatures from 35 to 85 degrees. They’re great algae eaters so typically subsist on existing growth within the aquaponics system. During winter they require less frequent feeding and produce less waste whereas in warmer temperatures.The average lifespan of koi fish is twenty-five to thirty-five years and Goldfish do not have filtration requirements that koi do.The average lifespan of a goldfish is five to ten years.

[Maisie Holmes]

It would be better if you had tell the water volume of you fish tank and plant container.

I have an assortment of shubunkins and other goldfish in a 1000L ibc tote, although the tote isn't quite filled to the brim so I have maybe more like 900L /ft. I have about 15-20 goldfish in there which seems like a low stocking density right now, but the fish are pretty small. In a few years, i expect to be fairly maxed out and I plan to add more grow beds for filtration. I dont monitor my numbers too reliably and enjoy a low maintenance system. I could probably stock more if i wanted to spend more time keeping an eye on it.

It seems to me like 15-30 is a good range for 1000L. although i would want about 2000L of growbed volume with 30 fully grown shubunkins for filtration. I would also want supplemental aeration and some solids filter. 

There are some basic rules of thumb around the forum here, mostly i think tied to gb to fish mass ratio