Fish feces

[Werner Kraeutler]

Dear Sylvia,

I do hope, reef fish excrete similar quantities of the different nutrients and metals. Please see the attachment.

Cheers
Werner

[George T]

Cool. We have fresh lake-caught blue gill on hand now and have been enjoying them at every meal for a couple of days. I've leaning heavily toward a catfish/blue gill combo for our system. If I'm able to hatch bluegill that will work as food for the catfish too.

TCLynx said:

I'm not sure about ease of breeding but one person I know said his blue gill did breed in his swimming pool system.

[TCLynx]

some one once told me that blue gill can actually get quite aggressive to predator fish when in tank culture. Would definitely need some further research but I believe there have been aquaponic systems that had poly culture with catfish and blue gill. I haven't tried them yet though they are good eating.

[Sahib Punjabi]

What wonderful and detailed information. Thank you sincerely for sharing :-)

Kobus Jooste said:

The picture I described to you about my vision for my systems is a combination of design desires and actual achivements. I have been able to take my systems off the grid in terms of water (rain) to some success - we are in the middle of a huge drought, and in some instances I needed municipal water in my research system, but the micro system has not been affected. Our systems can run on rain in any area getting around 200 mm of rain in a year. In terms of alternative sources for my systems in terms of power, I have design options but have not bought anything because of budget issues. I have been at it for over two years without a steady income, thus some things have to wait a bit. This is what I will do:
1) water temp regulation: There is a company here locally that has developed a low tech solar water heater as a pre-heating geyser inflow. It retails for under the equivalent of $500, pump, thermometer included. Only problem is that it is tuned to deliver water as close to 70 degrees celcius as possible. I will get myself one ASAP, and tune it down so that the pump kicks in as soon as the water is 24 degrees Celcius.
2) power: I use 70 Watts in the Micro, and a max of 120 Watts in the research system. Our 300 meter square system being built will run on 1.1 kW. Both the small systems can therefore run on PV panels and batteries. A friend of mine is busy developing a wind charger that can feed directly into a power grid without problems. I'm interested in trying that too. On the big commercial plans we have, we are very ambitious. My partners in that venture is an engineering company responsible for making auto assembly lines. They are busy developing linear fresnel systems that could power a large commercial venture we have designed and proposed to Government. They are interested, but we have not been able to get them to sign on the dotted line.

Fish: I'm heavily focussed on Mozambique tilapia. It grows larger than Nile, grows like weed at 24 degrees Celcius (75 F) and can survive 8 degrees Celcius (46 F) for a while. They are prolific breeders, thus getting your own stock going is simple. The stock needs to be improved a bit, as what is available now is not the prime genetics swimming in the wild, but I am working on that one and so are other people in the area.

Fish food: I want to work on 40 - 50 % lemna and 50 - 60 % BSFL. Lemna is our local type of duckweed - I use Lemna gibba. It is very special for a number of reasons - first, it is part of what a tilapia would typically eat, grows well until you let water temps hit 30 degrees Celcius, and can concentrate macro and micro nutrients in its cells at far greater concentrations than what is in the water. It also does not take up sodium, and is not affected by low levels of it in the water. Thus, in my research system, I am working on a mix of Mozambique tilapia (which can take full sea water salinity, Lemna gibba and a water mix that is doctored to contain all the elements plant and fish need to be happy. Lemna will grow, and this will be fed to fish in other AP systems. The wastes should resemble the data I have on aquaculture sludge on which we grow our plants in AP. The water will be doctored with a natural substance that will keep the process Organic/sustainable/all natural.

All that is left with to buy is the water treatments we normally get in - the pH control and buffering agents, and chelated iron if the Lemna does not suck up enough - yes, the plant can concentrate metals in its cells.

Seeds can be produced by letting a small number of your plants flower, and then moving them outside of your system to allow them to be pollenated without compromizing bio-security. We cannot buy pollenators or bio-control insects in South Africa at all.

Attached are some starter references. The first is an indication of what Lemna is capable of. The second gives you some idea of the macro nutrient dynamics in culture systems. The third one gives you a nice start on what, in terms of macro and micro nutrients, may end up in your system. As far as I can recall, animals do not need Molybdenum or Boron, thus those two you will not find in fish food. That is where the Lemna comes in. It is a vacuum cleaner of note - what is in the water will be in the plant.