(new here, first post)
We (my wife and I) are planning a new greenhouse this summer (in Michigan), and I'm in the planning stages of designing our first AP system. I had originally thought of going with one of the Nelson & Pade systems so as to skip over the guesswork of planning a system. But after much thought and research have decided that a media based system is best for us. I've spent hours reading through this forum and Murray's forum as well. Watched DVD's and looked at many different system designs here and elsewhere on the web.
Our plan is to start relatively small to learn what we're doing with AP, but size the greenhouse so that we can scale up and eventually (a year or more down the road) to fully feed our family of five, plus maybe a small CSA or farmer's market action... but that's a ways off.
So the thing I'm trying to get my head around now is the multiple fish tank question. With the Nelson & Pade system, they have 4 tanks so that harvesting fish only takes out 25% of the fish at any one time. I don't see any single systems here with multiple tanks, but did find a discussion about cages or dividers.
My current thought process is to build our starter system 1/2 or 1/4 size of what we'll eventually need (with an oversized pump), then after having some success with both the plants and fish, add another FT and another set of GB to the same system. Repeat as necessary.
Aside from the extra plumbing, and separate feeding process, would it be better to have 2, 3 or 4 smaller tanks, vs one larger one?
Thanks in advance for your input !
Well, depends on the fish you are going to grow too.
In a media based system where you are not removing the solid wastes, you are not nearly so dependent on fish numbers to keep the nutrients up for your plants since the solids are always slowly breaking down and providing more nutrients over time. A system where all solids are retained in the system requires less fish for the same amount of plant growth and you have some buffer if you were to empty the tank and not restock immediately.
But, How often is your family likely to eat a whole tank full of fish? And unless you get an aquaculture permit or set up a commercial fish processing facility, I don't expect you to be selling the fish to the CSA or market much. The primary reason for multiple tanks is for grading fish and harvesting a complete fish tank for sale but on a home scale system you are not very likely to grow enough fish to make selling them worth your while. You may still find veggie sales to the CSA or Market worthwhile.
Now I can see where more than one tank can be helpful but I can also see where having a couple totally separate systems can help if you were to have a disease outbreak perhaps it would only get one system rather than everything. I like fish tanks between 300-700 gallons. And I'm talking the actual amount of water in the tank since you really can't fill them to the rim and not expect fish to jump out.
I've got three systems. The big system has channel catfish in a 700 gallon main fish tank and a 100 gallon fingerling tank that has a bed next to it and that can be isolated when I get new fingerlings. I also have a separate tower system with a 300 gallon tank and in the back yard my 300 gallon system which is based on a 300 gallon stock tank as fish tank and then I have six 100 gallon grow beds being fed in sequence.
To make harvest easier you might look into crowding nets or happas nets that may also be able to help grade the fish as well. I don't think I would want anything larger than a 1000 gallon tank.
We usually just net out a few fish when we want them.
Thanks TC !
The point about the media system being less dependent on fish numbers makes a lot of sense (now that you say it ;-)
With that in mind then yes, having separate systems would have many advantages over multiple tanks in the same system. So we could start with our initial system then add a separate one later when we're ready.
Your first point really clarified things for me !!
I find that a 300 gallon tank is the smallest I would choose to grow out Channel Catfish in.
Here in Central Florida I recommend 300 gallon systems as the minimum for some temperature stability for flood and drain systems. The situation will of course be different for a Northern Greenhouse system.
Floating raft or constant flood will have more temperature stability but need more aeration and are more limiting on the plants that will thrive easily.
Ok - thanks for that nugget of advice too.
I know you switched to catfish due to their tolerance to cold compared to talipia. They sound like a good candidate for Michigan AP... How do they do for heat as well? I can imagine the water getting quite warm in the greenhouse in the summer.
More importantly... how do they taste?
Catfish and Bluegill are warm water fish, as in they grow well and have similar warm water tolerances as tilapia (though tilapia can survive some very poor dissolved oxygen and poor water quality that would put catfish into distress.)
Just make sure if your water is getting up much over 90 F that you have extra aeration and you should probably pull back a bit on the feed when things get really hot just because it will be hard to keep the dissolved oxygen high.
As far as taste, catfish is really mild (much like tilapia) and will take on the flavors of what you cook it with. As far as I'm concerned the catfish and tilapia we grew tasted pretty much the same and only had a slight texture difference. Tilapia when you overcook it will get stringy while catfish tends to get over dense when you over cook it. Otherwise the meat seems pretty much the same in my opinion. My Mom on the other hand, definitely thinks the catfish are far better (perhaps because a 5 lb catfish is far easier to get nice fillets from than an 8 oz tilapia. She hated how twichey the tilapia were to handle while processing even after being killed and in ice.)
Wow - so this is another salient point... that catfish are that much larger than talipia. How long does it take to reach this size?
Thanks again for your input.
Well, my climate plays a part in how fast I can grow catfish out large. But, In my first year of operation I started with rather advanced catfish fingerlings and the biggest fish we harvested that year was 6 lb. I kept a few fish from that batch for a second year and at the end of that second year I had a 10 lb catfish. Here in my warm climate (where the catfish usually only go off their feed for maybe a month after the coldest part of our winter outdoors) I expect to grow out catfish to a size between 3-6 lb in 12 months. Some grow faster than others, the real trick is managing to net the bigger ones when it comes time for a fish dinner.
The biggest tilapia I ever managed to grow was 2 lb and definitely most of the tilapia we harvested were between 10 oz to 1 lb 4 oz. Even in my subtropical climate I would have to heat the water a little just to keep the tilapia alive through the cold snaps in winter and if I want them to continue eating well I would need to be heating the water even in a greenhouse for at least 3 months of the year.
Where in Michigan are you from? I would love to know someone close to the Metro Detroit are who has the same interest as I do.