I would think that EDU cells could be easily made out of plastic bottles. In order to be reusable, all that would be required would be for the neck to be wide enough to remove the fully grown crayfish (yes, Yank here). That said, I quite agree with those who say this is nothing more than cage/battery farming. Do crustaceans care? From observation, I believe so. They actually do have distinct personalities and behaviors. But....that's a matter of ethics, not aquaculture.
My reason for posting here: I have been experimenting for several months now with a small-scale aquaponics, using a 20 gallon aquarium for the "aqua" portion. Water is circulated on a 15 minute on/off cycle through two gravel beds which contain various plants--approximately three complete water changes per hour (running it constantly led to overflowing in the gravel beds). At this point I am using a wide variety of plants in the hope of discovering which will thrive best.
I set out to build a "self watering indoor garden", planning to trap minnows or similar to populate (and contribute nutrients to) the fish tank. My system is, obviously, not large enough to produce food fish. When my traps caught nothing but crayfish (and one small catfish, who has taken a few nips but remains alive and well), I decided to give them a try. I read a great deal about keeping crayfish in tanks. Most of which, based on my admittedly brief experience, has proven to be wrong. For example, in articles referring to keeping crayfish as pets, it is commonly stated that 20 gallons of water are needed for one crayfish. I currently have approximately 20 of varying sizes in a 20 gallon aquarium which is less than 75% filled with water. In addition to water circulation, I have a 40mm air stone running continuously.
While crays are clearly territorial and mine do fight on occasion, it appears to be "show" for the most part. When introduced, they varied in size from 1-10 cm (approximately). None of the adults at this writing shows any injury or signs of an attack, and the little ones all appear to have survived and have grown. I have seen small ones crawling over much larger adults and for the most part they appear to be ignored.
I placed discarded plastic pipe fittings and pieces of pipe on the bottom to serve as "burrows" (no gravel in case I ever need to "vacuum"). They have taken to them quite well and in some cases have rearranged them to suit their wants/needs. At this point I have no plans to add more crayfish (at least for the present). If I did, I would also add more "burrows".
The major difficulty I am having at this point is that I do not seem to have enough grow bed area (or enough plants) to "filter" the water properly. The gravel beds keep the water clear and I am doing fine on Ph level, though I plan to add some limestone to the system soon. However, the current plantings are not removing all of the crayfish waste, or at least not enough to reduce the smell (the room my system is in smells like a late summer swamp). I am adding plants and if necessary will add more grow beds. All of the plants thus far appear healthy and some are growing at least twice as fast as they have in my experience with "conventional" planting. It remains to be seen whether they will flower and fruit when that time comes.
Similarly, I do not yet know whether the crayfish will breed in such close quarters (of course, I can always catch more, at least until the streams freeze over). I do have a small tank I will use as a breeding tank should I notice a female carrying a "berry". Surely I will have to replenish my stock at some point, though thus far my mortality rate has been zero. Obviously I do not expect that to last indefinitely.
Feeding has been no problem. Thus far I have been giving them freezer-burned or spoiled meat every few days, along with vegetable waste and expired canned goods (corn and peas) discarded by a local food bank. I have duckweed growing in the tank as well and they seem to like that--will "porpoise" across the surface to collect it. As long as I see "food" on the bottom of the tank I do not feed them. Thus far there have been no problems due to apparent food shortage.
I am using Orconectes rusticus or "rusty crayfish", an invasive species which has done considerable damage to fisheries throughout the upper Midwestern United States (they are native to the southeastern part of the country). They are larger than the common crayfish native to this area and have in large part displaced them since they are more aggressive and destroy aquatic plants which serve as spawning beds. They will, by and large, eat anything. Characteristics which are dangerous in an invasive species but useful in captivity, so long as they are not aggressive toward each other which they do not appear to be.
I would be interested in hearing of the experiences of others in using crayfish basically as "fertilizer makers". Mine are currently supporting approximately 40 (for the moment mainly small) plants and could feed more based on the nutrient level in the water. Provided the population remains stable, I suspect I could add two more growth beds without difficulty.
I hope to hear from others who have had experience. And if anyone has managed to produce sufficient crayfish to generate a food crop, I would like to learn more about that. What is your tank size? What sort of population density? And how much surface area should be required for filtration/plant growth? I presently have more than twice as much surface area dedicated to filtration/plants as I do to the crayfish tank, and it does not appear to be enough.
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