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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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Wow!  That's the first I've heard of catfish eating plants!  Darn darn darn....thanks for sharing that very important bit of info.  Back to the drawing board!

Barbara Mumpower said:
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.  
catfish love to eat crayfish!  ;)

Kate Mink said:

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!

If you are afraid of the catfish disturbing the roots you could  build a barrier from bird netting to separate the roots from the fish.

I wonder if you kept the trough flowing at a high flow rate it would help flush the tank of solids. I notice that river caught catfish taste better than lake caught catfish. Maybe swimming against the current makes them taste better.

I was just thinking about some sort of plastic netting.....but then it would be another complication to get in the way of netting or corralling the fish.  I'll have to think about that a bit more.

Yes, my idea for having catfish or trout in a raft bed was so that I could create a swift-flowing stream-like habitat where solids would be swept right out.  I'd wager that the difference in taste between a river-dwelling fish vs one from a lake is simply due to a difference in diet and the water itself.  Fish that are drinking murky water have an earthy taste....they taste like the dirt they are drinking!

Chi Ma said:

If you are afraid of the catfish disturbing the roots you could  build a barrier from bird netting to separate the roots from the fish.

I wonder if you kept the trough flowing at a high flow rate it would help flush the tank of solids. I notice that river caught catfish taste better than lake caught catfish. Maybe swimming against the current makes them taste better.

Averan the chinese have been growing Koi and carp species under floating rafts for years. From the videos I can only guess that they have very low densities and large raft systems. I think if you have an abundance of feed the cats and or bluegill would be fine in small numbers. Would lean towards gravel in the bottom of the raft to lock up sediment and give extra room for bacteria. I will tell you that you will be limited to short term crops. I dont care how low your stocking is a tomato or cantelope will struggle with the sediment on the root. Definitely do this and experiment with different designs. Make it flexible so you can change things. My rafts are a fun addition to my system but I am downsizing them to make room for more gravel beds. The beds just perform better for a non commercial grower. The beds are way easier and can grow more varieties in my system the way it is set up. I have tried to grow several crops over my fish tank in rafts and it has been a blunder. No success as of yet. Still trying to find a crop that can handle the ammonia and high sediment.

My koi have completely destroyed any aquatic plants I have had in their tank, so I only assume they would continue the same behavior under rafts.

Lots of good thoughts there....the current design I am working with has 3 26' beds.  Only the central deep one with the fish is a raft bed, the other two are flood/drain media beds.  So I've got about a 2:1 ratio of media to raft which will be more than enough bio-filter for the fish wastes.  The space I have to work with is on a hillside so it presents its own challenges, but I really am liking my idea of a using the lower bed as a combination sump/media bed.  As it drains, the uppermost bed is filled until it triggers the siphon, which then floods into the middle raft bed with the fish.  Of course I'd plumb a line directly into the raft bed from the sump in order to maintain constant flow in addition to the surges from the upper media bed draining.  I don't want any gravel in the raft bed because I want all solids to flow out and into the sump/media bed below.

Also, because the site is only accessible by foot after descending a whole lot of narrow steps, I'm not too keen on lugging bags or buckets of media for the thousand or so trips it would take to fill those beds!

I have been sketching this up with versatility in mind....media beds could become raft beds, but it would be hard to convert a 3' deep raft bed into a media bed without supersizing the sump.  But the combo of 2 media beds to 1 raft will let me grow a good collection of different crops.

Thank you for your helpful thoughts! :)


David Waite said:

Averan the chinese have been growing Koi and carp species under floating rafts for years. From the videos I can only guess that they have very low densities and large raft systems. I think if you have an abundance of feed the cats and or bluegill would be fine in small numbers. Would lean towards gravel in the bottom of the raft to lock up sediment and give extra room for bacteria. I will tell you that you will be limited to short term crops. I dont care how low your stocking is a tomato or cantelope will struggle with the sediment on the root. Definitely do this and experiment with different designs. Make it flexible so you can change things. My rafts are a fun addition to my system but I am downsizing them to make room for more gravel beds. The beds just perform better for a non commercial grower. The beds are way easier and can grow more varieties in my system the way it is set up. I have tried to grow several crops over my fish tank in rafts and it has been a blunder. No success as of yet. Still trying to find a crop that can handle the ammonia and high sediment.

Generally with raft systems you run the water from the fish tank to a settling tank. I use a barrel for my large system and a laundry sink for my small system. There's a divider separating inflow from outflow; that slows the water down even further. I can suck the accumulated sediment out with a wet vac and dump it on my dirt beds. Overall a slow flow rate works fine, allows you to use a smaller pump, and even more fine sediment drops to the bottom of the trough. Having Gammarus (water fleas) in the system also helps keep the roots clean.


I'm thinking of adding Gambusia and Tetras to my troughs to eat mosquito larvae; they don't eat roots.  I've gotten small tilapia in my troughs before and they're VERY hard to catch.
Averan said:

I was just thinking about some sort of plastic netting.....but then it would be another complication to get in the way of netting or corralling the fish.  I'll have to think about that a bit more.

Yes, my idea for having catfish or trout in a raft bed was so that I could create a swift-flowing stream-like habitat where solids would be swept right out.  I'd wager that the difference in taste between a river-dwelling fish vs one from a lake is simply due to a difference in diet and the water itself.  Fish that are drinking murky water have an earthy taste....they taste like the dirt they are drinking!

Chi Ma said:

If you are afraid of the catfish disturbing the roots you could  build a barrier from bird netting to separate the roots from the fish.

I wonder if you kept the trough flowing at a high flow rate it would help flush the tank of solids. I notice that river caught catfish taste better than lake caught catfish. Maybe swimming against the current makes them taste better.

People use solid-settling tanks because for some reason they don't want any media beds in their raft-only system.  All those discarded solids are a wasted resource that could be turned into more fertilizer for the plants.  I think this attitude is a hold-over from traditional commercial aquaculture and this is an area I am trying to innovate.

Well in some cases the commercial operations are trying to maximize fish production and to do that they have to remove the solids so that the system can keep up with the biological oxygen demand.  It would require lots more plant space to keep up with the systems where solids are retained.  Or the way most backyard or veggie centric growers see it, it takes far less fish/fish food to support the same amount of veggies.  Just different priorities I think.

 

As to the catfish eating roots, I've not seen it but I've also never put a raft over my catfish.  However, fish sometimes get curious and I have seen my catfish grab hold of things and tug if there is something like a string hanging down into the water.  So even if they are not eating the roots, it doesn't mean they won't do damage.

 

Here is an idea that might be more useful.  In the raft bed (and I would definitely go much deeper than 18 inches) you could fence off one end where the fish could live and put a solid raft over it with wicking mat on it for starting seedlings so the roots wouldn't be coming through for the fish to eat them.  So the fish wouldn't have the run of the whole trough but they could live under the propagation area?  Would that solve any problems?

Yes, different priorities...which is why it's good to question some of the taken-for-granted practices just to be sure.  ;)

I have thought about dropping in some net wall dividers in the bed to break up the trough into different size fish.  And I have been thinking of starting my raft seedlings right in the same trough, just because for my situation it is the best use of space.  It would make sense to have the seedlings and biggest fish at the outlet end of the bed....big fish, small roots, least nutrients.  Then I could hold the fry up at the inlet with the mature plants.....small fish, big roots, most nutrients.  Additionally, with the big fish closer to the outlet, their waste won't spend as much time in the tank/bed before exiting.

Perhaps confining the fish to a smaller area might solve the issue.  I wish I could give them more space to roam, just for my own peace of mind.  :D

If I didn't have such high summer temps I'd just raise trout and not worry about my roots at all, but catfish seem like the best bet for my situation.  Trout live in our local streams and rivers, but not on my sunny hillside!

Who says the solids are discarded? I put them on other plants growing in dirt - and truthfully, in a yearly cleaning i collect only about a half gallon of deposited solids. These can also feed prawns and the helpful water fleas right in the trough. Waste not, want not.

Averan said:
People use solid-settling tanks because for some reason they don't want any media beds in their raft-only system.  All those discarded solids are a wasted resource that could be turned into more fertilizer for the plants.  I think this attitude is a hold-over from traditional commercial aquaculture and this is an area I am trying to innovate.

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