Goldfish vs koi in the pond

[enrgizerbunny]

Hello. I currently have no pond, but would like to install one this time next year, and stock it the following spring. I also have two aquaponic setups that will have goldfish as the work horse.

Now, to my real point. Aside from my outdoor pond which will be considerably smaller, I want to build one in my future greenhouse. The design will be for aquaponics, so I want to stock it a little heavy. The dimensions I'm thinking at the moment are along the lines of 4'x8'x1.5' which comes out to just under 350 gallons.

What is your opinion on keeping some koi in there? What is their bioload like versus goldfish? How fast do they grow out? How many could I stock?


I have someone who will gladly take them when they out grow my pond, and they have a pond you can canoe in.

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[jlk]

Honestly, there is a bit of a difference between stocking a bit heavily and stocking that may be a bit unrealistic. I would expect koi to outgrow this in approximately 4-6months (possibly less) with an excellent diet and frequent wcs.

Could they be kept in this setup for the purposes of growing them out for a bit? Yes, but I am not positive in would be an ideal setup for an aquaponics tank situation. While the fish would provide the nitrates for the plants, the water would need to be buffered to a degree (many plants prefer acidic conditions) and wcs would still be frequent and necessary to limit hormone accumulation. Plants alone may not be sufficient filtration. I would also be a bit concerned that they would jump from a minimal depth pond.

Its great that your taking your time and doing your research for what is going to be an interesting project! I would definitely spend more time researching and talking to others with these type of setups to figure out what types of fish would be most appropriate to provide a good balance between fish and plants without overwhelming your system. Good luck with your project!

 

[pip walters]

Aquaponics is a great way to grow two crops - plants and fish. I would pick a target saleable size for my koi to be able to sell them, then stock accordingly with juvenile fish.

I am sure you have researched water management for aquaponics.

At 23C, which is optimal for carp growth, I would expect a 2-3" koi to grow to arund 6-8" in six months easily with correct feeding. They will need between 2 and 4% of their bodyweight in food per day. I used a computer spreadsheet to calculate daily feed rates based on expected weight gain when I was farming common carp, koi etc. If you go ahead and need further advice on feed and feed conversion rates, please let me know.

 

[enrgizerbunny]

Well many have had good results with goldfish. I'll be using them in my other setups.

What exactly do you mean by buffered to a degree? I purchased an aquaponics system off Craig's list that came with potassium carbonate that he said he was using as a buffer. Personally I use crushed coral in my tropical tank and the 10 gallon that is yet to be a platy tank. I'm not sure about potassium carbonate as a buffer, but I know I use it to adjust PH if I get into a funky situation and I need an immediate water change and don't have time to aerate the tap water. It only takes a few teaspoons to bring up a PH of 6 to 7.2 in 30 gallons of water.

I'll be collecting rain water in barrels by the time I build this "pond" so it should be neutral. My tap water is too acidic to do water changes without aerating, and it raises a whole point in PH when it gasses off.

As far as depth is concerned, how deep would you recommend? 30 inches? That would increase me to nearly 600 gallons which would require A LOT of grow beds(which isn't bad, more food!) to achieve sufficient balance in the system, or I would need to lower my stocking to accommodate for the lack of beds.

What is the about hormone build up?I had no idea.

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[pip walters]

The reason for using potassium and calcium products as a buffer is that it raises the pH using minerals that the plants can utilise. It doesn't make any difference to the fish, as long as the pH is to their liking as they very little of the mineral content directly from the water, they take it in their feed.

I am sure you already know you will need biofiltration to produce the nitrate and phosphate your plants require. There won't be any hormone build build up unless a hormone enhanced diet is used as in some food fish intensive culture. The whole point of aquaponics is that it is organic, therefore eliminating such allocthanous input as hormone enhancement. Even the solid waste can be collected and used as fertiliser elsewhere. It is also very water efficient as the plants use the nutrients and micronutrients that we try to reduce in aquaria by performing water changes, thus requiring just top-ups to replace evaporation and transpiration via plant leaves.

You should be able to calculate the amount of ammonia and therefore nitrate you can produce for your plants based on the required amount of fish food given and from that, I would hope you could calculate the number of plants of your chosen varieties that you can produce. I am sure there will be info like that available somewhere.

It sounds like a very interesting project.

 

[jlk]

Make sure you test your rain water on a frequent basis. Depending on your locale, it may be very acidic. Using rainwater is great but just make sure it's properly remineralized and buffered as rainwater is nature's distilled/RO water.

In respect to hormones, I am not referring to hormone enhancement as Pip mentioned (which I feel is manipulative and unethical) but to the hormones levels fish naturally produce that can induce stunting when in close proximity. These can only be removed via wcs. Look forward to seeing pics as your project progresses!

 

[pip walters]

My understanding is that growth hormone in fish is involved in many processes other than growth and it is prevention of the release of growth hormone within a fish' s bodily system, because of stress factors,(such as overcrowding, poor water quality, poor diet etc or a combination of all of those) that prevents further growth and the fish remains small (stunted).

Certainly in my small carp, there were always fish that grew faster than others and some that remained smaller in general, but rarely did any of the slow starters fail to grow at a much faster rate when stress factors were reduced - I.e. when they were stocked out into mud ponds.

I believe that poor water quality is a much more important factor in reducing growth in fish than overcrowding or lack of space. It has been shown many times that fish (certainly Cyprinids at least) can continue to grow normally in a small space as long as water paramaters and food quality are optimal.

As far as I know, the theory that fish release a growth inhibiting hormone that can affect stunting in other fish in close proximity, has not been proven and has arisen through a misunderstanding of the role of growth hormone. What advantage would a fish gain in normal environmental conditions? If anyone has scientific info to the contrary, I would love to read it as this is an area I have great interest in.