Aquaponics - High density marron farm idea

I've had a few more thoughts on a high density marron farm, and they seemed to have coagulated into something that looks a little like this.

Side view - High density  marron farm idea 

The water and solid fish waste would flow from the fishtank into a flow splitter made from an 8 inch PVC pipe connected at right angles. The flow splitter would then be connected to a number of 8 inch PVC pipes that would slowly take the flow to the growbed.

Each PVC pipe would contain a number of different baskets that could move freely along the PVC pipes.

Each basket would hold one marron. The largest marron would be those closest to the fish tank, and these would get first bite at solid fish waste, and uneaten food. As the feed and solid waste moves to the right, the other, progressively smaller marron get a chance at it. Mature marron would be harvested from the end closest to the fishtank, and new small marron would be added to the system at the growbed end. Each marron would be in a separate basket to prevent fighting.

The water would enter, and move through the system via gaps at the bottom of the baskets. To maintain water in the pipes, the water would exit the pipes at the top.

Top down view - High density marron farm idea

Seen here from the top, we see the flow rate from the fish tank would be very slow because of the large diameter of all the PVC pipes. This would give the marron several chances to catch passing food. The total flow through the system is the same as it would be without the marron farm, but because it's spread over such large pipes, the flow slows.




The length of the marron farm pipes would depend on how many marron your system could support.

Using this or a similar system it should be possible to grow marron (or whatever underwater walking things are called in your part of the world), in an aquaponics system without all the cannibalism that can come with underwater walking thing farming. This marron farm would be placed in the following order of flow...

•  fish tank
•  marron farm
•  swirl filter
•  grow bed

Small marron might be kept in an aquarium, and only the largest of the batch might be added to the farm each week. Grading out only the biggest marron might prove difficult so I might have to come up with a way to trap the biggest and let the others through unhindered.

Or something.

I'm not sure if this is the solution for me. It's just an idea that was rattling around in my head, so it had to come out.

Aquaponics - Marron stocking density

I'd like to grow some marron but they eat each other.

One of the issues with things that use their claws to catch and kill things, is they tend to use them on each other, or their young.

Marron, for those who don't know fall into the "things with claws that walk on the ground under water" category. They also fall into the "delicious" category.

The problem is that, because they eat each other, you cant keep many in an aquaponics system. Given a choice, marron would like to be left alone and hangout and eat. The problems arise when they go looking for food, or a mate, or when the just go out for a stroll and bump into another marron also out for a stroll.

One solution is to give them plenty of hides in the form of hundreds of short lengths of PVC tubing. Which sounds like a good idea because I seem to love using PVC tubing, but I'm not sure if it solves the bumping into each other problem.

Another is to only populate one marron in each half square metre of fish tank bottom space. That would only allow 2 or 3 in a 1000 litre system, but allows each marron to back away from more aggressive marron they meet strolling around. I'm hoping for stocking densities that might allow 30 or 40 marron in my new fish tank rather than 2 or 3.

Yet another solution I have seen, was to create high rise housing that float around in a fish tank where each crustacean (yabby in this case) has its own space to stop them killing each other.  The yabby spaces where stacked on top of each other so that in a one metre deep fish tank, there might have been ten stacked on each other. These yabby buildings floated around in the current. The problem I see with this approach is that unless there is a great deal of turbulence in the water, the feed might never meet the yabbies. In the system I have seen video of, there seemed to be a great deal of wasted food that simply got filtered out of the system, and dumped.

Other than the feed issue, the marron high rise seems like the best idea. I think I'm leaning in that direction, but perhaps with a way of feeding each "building" via a tube that runs down through each marron's house, so that each marron gets a share of the food, and nobody misses out.

I'm off to buy a fish tank or two tomorrow, so I want to design a system that includes marron before I start building my new bigger aquaponics system.

My research continues.

Aquaponics - Marron

Apparently, marron come in two varieties. Hairy and not so hairy. Cherax cainii (smooth) and Cherax tenuimanus, or Margret River marron (hairy).

fine marron illustration*

Marron are a fresh water crayfish, native to Western Australia. They are a good candidate for farming because they have a good food conversion rate, so they grow well and don't cost too much to feed. They can grow up to a weight of 2 kg but are usually harvested for sale at between 100 to 200 grams at a little under 2 years of age. Marron rank equal to the highest percentage of meat to total body weight for similar under-water walking things.

They are active mainly at night, and are opportunistic feeders that will eat whatever they find. In the wild the majority of the food comes from plant material, small living and dead beasties, and detritus (decomposing plant matter colonized by fungi and bacteria.

They thrive in water temperatures ranging from around 13 deg C to 25 deg C. Water temperatures over 30 deg C will result in deaths.

Marron need a quarter of a square metre of space each when grown in a conventional dam or similar, but it may prove possible to increase the possible population density by using a multi level hi-rise approach, or with the addition of a stack of short lengths of PVC tubing to increase the available surface area, and allow lots of places to live and hide.

In order to grow, marron find a safe place to hide, then spend some time shedding their hard shell. Once shed, they expand into their new softer shell and go back to their normal lives until outgrowing themselves again. They may appear sluggish and generally disinterested in the world when about to shed their shells. If this happens, leave them alone and don't try to cheer them up by feeding them. When changing shells they go off their food for a while, and continued feeding runs the risk of fouling the water. As with all aquaponics feeding, feed only what is eaten right away, and stop feeding if food is left uneaten.

Marron can be grown in tanks or ponds as shallow as 20 cm, but beware their climbing and escaping abilities. Like other similarly shaped critters, they can walk on land and will wonder off in search of a good time if allowed to do so.

Marron don't like the sores they get on their undersides from bare concrete tanks so add something soft like sand, or fill the bottom of their tank with PVC tubing.

Apparently marron like to eat worms.

They also enjoy the type of pH levels found within aquaponics systems, and have a particular fondness for pH levels of between 7.0 and 8.5. They are found growing in the wild in water ranging from pH 6.0 to as high as pH 9.0.

Fresh water is best but they can tolerate saline levels of up to 15 parts per thousand. They thrive in salinity levels of less than 5 parts per thousand, and wont breed in higher salinity water.

*actual marron may have legs.

Aquaponics - Fish

Aquaponics - Fish

Fish! Vegetarians, this page might not be for you.

The swimmy, tasty side of the aquaponics equation is fish. Depending on where you live there are a few different options. Talapia might be one if you don't live in Australia. Statistically you don't live in Australia. If you did live in Australia, and you grew talapia, you might get into a stack of trouble. Talapia are a pest species for all of the reasons that make them a good candidate for aquaponics.

Catfish. I know nothing about catfish but it seems like they are a candidate for aquaponics. Other species that might be worth a look are Cod (angry, eat their young), Barramundi (warm water), Jade perch (highest omega three), Goldfish (only swallowed whole by 50's youth in TV sitcom "Happy Days") and various things like clams, and walking things with claws(whatever they may be called in your part of the world). Basically, from what I've read, if it poops and lives in fresh water you can use it. But if you don't intend to eat it I would think goldfish would be your best bet.

Check your local laws, but good candidates for edible species include...

Talapia are a very popular fish to grow in an aquaponics system because they cope with a wide range of water conditions, they eat everything and are apparently good to eat, they breed readily and grow quickly. If they are legal in your area, from what I've read they seem like the best choice as long as you have warm water. Talapia covert food into fish very efficiently.

Trout. If you are in a colder part of the globe you might try trout. Trout enjoy water that's less than 20 deg C. Its often possible to grow trout as a winter crop as they grow very quickly. Trout are often farmed commercially and are known for their conversion rate of feed to harvested fish fillets. ie It takes a relatively small amount of feed to grow a trout. I think that's because they do a lot of sitting still.

Carp are another pest species for Australians so are a no-go area for me. They are full of bones and taste like mud. Many Australians have a poor relationship with carp because we think they are full of bones and taste like mud. Australians also thought they tasted so good that they would import them from Europe and release them into waterways, causing insane damage to eco-systems that were poised on a knife-edge of sustainability just by virtue of being in Australia. Full of bones, mud.


Yabby. The yabby is delicious. As are marron. I'll be trying to grow some yabbies and/or some marron.
They breed in captivity, eat scraps of food left by other fish, and generally clean up your fish tank. I am trying to work out a way to keep them separate but living in the same fish tank.

[more in this post on marron]

Silver perch. Silver Perch seem to be the most suitable species for me to grow based on my location. They are good to eat but are a little slow to grow. They have high levels of omega three fatty acids, whilst retaining a clean white flesh. They are omnivores, and will eat things like lettuce and duckweed (a very small, floating plant I'll try to grow in nutrient rich barrels of water for fish food) From what I can gather they can take a wide range of water temperatures but might not grow much over winter. They also tolerate a wide range of water pH. If all goes well, I should have fish for the plate within 18 months, and then have a constant supply after that. Silver perch seem to get along with little silver perch without all the cannibalism that comes with some other species so I'm hoping to keep 3 or 4 different ages of silvers all in the same tank.

Not just Aquaponics - Fish, http://120thingsin20years.blogspot.com