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I'm in the early planning stages of building a bigger system and I'm looking into ways to save space and reduce the need for a dedicated fish tank.  Can anyone tell me if catfish tend to eat plant roots?

Does anyone know of any good reasons why I shouldn't keep catfish in my raft beds?  It seems to me that if I make my beds a little deeper, say 18" or so, that I could easily have a bunch of catfish in each bed.

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I have not tried it but catfish would probably eat the roots of your plants. I KNOW FOR A FACT that tilapia will eat roots,plants and anything else they can get their lips on.

I know all about Tilapia, but haven't heard whether catfish do the same.  The fact that they are bottom feeders suggests to me that they would leave roots alone, especially if given other food sources.

What will the catfish be eating?

 

The biggest problem with having fish under rafts is how do you maintain the fish when they are covered from view with foam and plants? To get to the fish you will have to remove rafts which will be extra work at a minimum but you will probably damage roots in the process. There would need to be somewhere to put rafts while working with the fish. You will have to remove all the rafts to harvest fish. If any rafts were to be left the fish will hide under them.

When(NOT IF) a fish dies it will rot under a raft until you discover it. I just about crashed a system when a large tilapia died in the bottom of my net tank and rotted for a long time before I discovered it. The rotting process removed all the DO from the water going to the troughs and the plant growth almost stopped. The point is if you cannot see a floater you cannot remove it in time.

The amount of feed changes with the growth of the fish. Monitoring of uneaten feed is VERY important so adjustments can be made for the next feeding. This can't be easily done when the fish are covered regardless of the type of fish.

Fish under rafts could eat or compete with the beneficial organisms that live in the roots of the plants and in the sludge at the bottom of the trough. Most raft growers like myself rely on the microorganisms in the troughs to keep roots clean. If a fish was trying to get to the bugs in the roots there would likely be root damage.

Hi Averan,

Great points all Chris! For backyard application with small number fish/plants where production is not a major concern you can run a trial on this. Most raft generally have liners which are smooth sided and are probably the least impressive surface, compared with other conventional AP media to encourage bacterial growth, as a result most of the bacteria accumulates at the bottom of the troughs as sludge.This "sludge" has some volume but is loosely attached to the liner and because of the slow movement of water in the trough settles and stays at the bottom. I'm wondering if we put fish in the trough this will stir up this sludge and allow it to move through a circuit from bed/tank if it could affect the density of bacteria.I know that bacteria evolve and grow into a matrix, could this movement diminish them? I know this would change the water clarity as well, which may not be of great concern to some. What about the fish waste? Normally the waste would be able to "fall out" and settle as water travels along the length of the raft, but with fish keeping sediment in constant flux the suspended waste may start to adhere to the plant roots slowing their growth and eventually even destroy them. Mind you, all this is just speculation and only someone with this experience will know for sure, so go ahead give it a try!

Thanks all.

My goal is to actually set this up mostly as a vermiponics system, so the catfish living in the troughs are filling a niche, but not the driving force for nutrient generation.  I would feed them fish food, but hope that they would also consume some of the worms and soldier fly larva that flush into the troughs.  As Harold mentioned, I thought that having catfish swishing around in under the rafts would help stir up sediment and keep it moving down and out of the trough.  This would not be your typical raft system and I would not need to rely on bacteria in the troughs.  I would have plenty living in the flood/drain worm bed full of gravel as well as in the pond-like sump.

I have space for 4 x 30' beds with room for separate worm bins/beds and the sump.  That's the max available, I may start smaller.

As for harvesting fish, I don't really plan to do that often, but when I need to, I would use a technique similar to the Friendly's method in their circular tanks: lay netting along the bottom, then slide a pole underneath from one end to the other to isolate the fish.  Of course I would need to lift rafts along the way.

The dead fish issue is a good point.  I wonder if other catfish would eat it?  or maybe a crayfish?  Uneaten fish food would be consumed by the other little critters populating my system, particularly in the pond/sump/marshland.

Thanks for the thoughts.  This will help a lot as I continue to explore and design this hybrid experimental system!

Hi Averan,

 

I suspect you may need to consider that the essence of the recirculating system is that it allows the process of settling, filtration absorption etc to take place while the water slowly moves through the system. I suspect that without the movement of the water the process may be hindered somewhat. I wait to hear the results of your experiment though.

Those functions are taken care of in the system, just not in the raft beds.

I'm still in the design/sketch phase of things, but at the moment the components I'm considering are:

  • flood/drain gravel worm beds (main source of nutrients is from compost collected in the neighborhood)
  • DWC raft beds w/ catfish (high-flow, little extra nutrients from fish poo, fish eat worms/bugs)
  • sump (bed turned into a marshland pond w/ some plants, water plants, clams, crayfish, gravel/sand, etc)

No one has really tested a vermicomposting system like this before so I'm on my own.  I am still trying to figure out how or if this will even work.  A typical worm bin sits for some time while it produces that brown tea slurry.  With my setup, the worm bin would be flooded and drained constantly which would not allow the tea or slurry to build up and concentrate.  This should help prevent buildup on the plant roots.  Then again, all I need to do is introduce something like the Gammarus to fill the niche of cleaning plant roots.  As much as possible, I really am just replicating nature, making sure to create a diverse and balanced ecosystem.

 

Hi Averan,

I think you've got something good going here, it may take a little time/thought to figure the right component-worm-plant-media ratios to create a balanced AP, but definitely doable.

for sure!  I spent months designing my custom micro system for my balcony!  thanks for the encouragement.

Here's a quote from Friendly aquaponics FAQ on crayfish (with different spelling): "If you grow crawfish in your system, that's all you will be growing for ever and ever. They are like piranha with opposing thumbs, and they take WALKS at night across country to other ponds/streams/aquaponics systems nearby and colonize them. They are nearly impossible to get out of an aquaponics system once they're in there. ... Be REALLY careful with crawfish!"

They do have good results growing freshwater prawns in their troughs. These are related to crayfish, but very different behaviorally.


Averan said:

The dead fish issue is a good point.  I wonder if other catfish would eat it?  or maybe a crayfish?  Uneaten fish food would be consumed by the other little critters populating my system, particularly in the pond/sump/marshland.

Thanks for the thoughts.  This will help a lot as I continue to explore and design this hybrid experimental system!

Hi, I can tell you from experience that catfish will eat every root they can get.  I am trying to get a raft system off the ground.  I have the fish and one run of raft system. As a temporary place for my plants, until I could get the first trough finished I put my rafts directly on the pool where my catfish are.  The little buggers not only ate the roots, but, where they could, they pulled the whole net out peatmoss and all.  

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