Backyard Aquaponics
A place to discuss aquaponics

We have an aquaponics system up and going for a couple of months now, and everything is going fine (so far). We've been using Ridley fish pellets as food for the fish and they seem to thrive on it, and I understand that it is a complete source of nutrients for the fish. If we started growing duckweed, would we need to keep supplementing their food with pellets or some other food source? Has anyone else gone down this path?

Hi Mycopathalogica, good to see you here...

From what I understand duckweed can be used as a large percentage of a fishes diet. Of course this depends on the type of fish you have in your system. If they are herbiverous or omniverous, like goldfish or silver perch then you'll have no problems supplementing a fair percentage of their diet with duckweed. Barramundi are carnivorous and won't eat it, but you can feed the duck weed to worm so that it's converted into something the barra will eat.

My new system is going to rely very heavily on feeding duckweed to the fish, but I haven't fed any fish large amounts as yet, the problem seems to be growing enough of it at the moment to feed my fish....

How is your system set up Myco, and what sort of fish have you got in it?

How do you prepare the duckweed? (or do you just chuck it in?)

Just chuck it in....

Scoop it out of the duckweed growing ponds, with a net, then tip it into the fish tank.. I haven't actually seen the fish go into a feeding frenzy over it, but they certainly eat it, as it all disapears within an hour or two..

This is only through the brief trials I have tried so far, I haven't had enough duck weed to really give it a decent go and watch how the fish go with feeding on it over a longer period of time. The duckweed/yabbie side of my new system should be up n runnning this afternoon for the first time, so with a bit of luck I'll be able to get a better idea soon of how much the fish like a diet of duckweed as I slip into top gear duck weed production.

Duckweed sure does multiply quickly. I bought a small zip bag of it on ebay. Only took a few weeks to cover my pond surface (120cm diameter).

Suposed to be able to double it's size each day, which would make it very usefull in feeding fish..... Once you've got it you never get rid of it though, unless you have lots of fish that will consume it..

And I think I mentioned it once before, but I'll mention it again to everyone. Don't put duckweed into any pond/dam/tank that any type of water bird (ducks/stocks/egrets etc)may visit, the duckweed sticks to them, then they fly off to other natural waterways and seed them with the duckweed...

Hi folks

I was looking at the protein content of duckweed and the protein content of the waterfern azolla.

Seems that the way to do this is to grow them up in shallow buckets or trays and add cow manure to the water. Say 5 %.

Apparently this will boost the protein levels in duckweed to amazing levels - 40 - 45%. I would imagine that Azolla would respond similarly.

Duckweed and azolla therefore have great protein content - (on a par with soyabeans, peas and lupins) if raised correctly and can double their biomass in 2 to 3 days.

I have recently been grabbing a small handful of duckweed and azolla and just crushing it in my hand to a paste before throwing it in my tilapia bin. They don't get all excited by it, but it gets eaten.

I give them a little goldfish flake in the evening, followed by a little ground pig food, micro worms now and again, a few compost worms, some rabbit droppings occaisionally, and in the morning they get the azolla and the duckweed.

I am going to try and stop the flake when the small ones get a little bigger and then feed them mainly on Azolla, duckweed, any other veggies such as eggplant and lettuce, and composting worms. Hopefully this will mean that they cost me nothing at all to feed.

Apparently duckweed and azolla are the ideal fishfood for tilapia - but I think a little variety thrown in will help regards overall health and access to a wide spectrum of vitamins etc.

I have just set up two bins at school to take 10 tilapia each. I am just waiting on a couple of heaters. If I get my act together one will be fed duckweed and one Azolla.

(I was going to do rabbit poop, but I think the protein level is too low at 15 - 18 %.

Will be interesting for sure.

Don't forget the protein content is almost always quoted on dry weight.

See Previous thread for disussion

Steve

Yep .. Steve ..

good point!


thats is crude protein .. (dry basis)

Amount of protein divided by the amount of dry matter multiplied by 100.

If it were quoted on a wet basis .. it would not be useful info in this case.

However this is what I don't really understand ...

Azolla - 40 % protein (dry basis) perfect tilapia food apparently ... .. also 90 % water .. so I guess they have to eat a hell of a lot cos azzolla is 90 % water ..


Proprietary dry goldfish flakes - 40 % protein (dry basis) .. fed as a dry meal ... get fat real quick?

Dry pig food 25 % protein .. 3 % water ... is that better than a veggie meal - 90 % water .. eg. mashed lettuce?

They eat less pig food ... but get more protein per mouthful .. even though the protein content is ony 20%

Is dried duckweed better than fresh duckweed?

Dried duckweed will have a highr protien content on a dry basis.

Say both are quoted at 40 % protein (dry basis).

I don't really get it?

Thanks Steve .. you sure get me thinking and have great ideas!

COOL!

Unless Gary has some specific info, i'd not bother with drying duckweed.

Its probably done for storage and transport, and i reckon that you should leave thing as close to nature as possible, especially if its easier

Steve

Some websites suggest that wet Azolla or duckweed (not dried) are a great performing food for tilapia. Another suggests that it is not good at all.

I have also read that Spirulina is the best food. Is it easy to grow? I understand that it likes pleanty of air, and likes a fairly alkaline pH (similar to Tilapia!)

How does Spyrogyra or chloralla compare?

Where would you get cultures of these microalgae?

Just a thought, growing algae can't be that difficult can it?

They are only a good fish food if you have filter feeding fish though Johnnie..... Ohhh thats right, you do.... If you really want to get hold of spiulina, or some of those others, you may have to try a university or similar.... And while your at, see if you can pick up some of that oil producing algae that stands to be the most intensively productive oil producer ever found...

Jade perch loooove duckweed.
Yesterday I purchased a plactic bag full of the little weed from the local Aquarium Shop - about a cup full compressed.. $4.50......I put about 2 tablespoons into the fish tank before putting the lid on for the night.....this morning the only duckweed left were a few stray lone duckweeds sticking to the edges of the tank here and there..... I have put the rest into a pond at the front of the house, so I hope it grows as fast as is reported. I think I will have to get serious about a few drums etc to grow the stuff as fast as possible.
Murray
Sorry earthbound, not sure where to post this comment.

Growing the duckweed is so simple Murray, The half drums I have started using seem ideal. A couple of goldfish to keep down the mozzies, add a bit of fertilizer of some sort, carlie carp, manure etc, and leave it in the sun... I'm very keen to see how much I can produce in my barrel setup, and I'll be weighing it to know exactly how much I'm getting..

If you ever made any dud growbeds they would be ideal for duckweed production. Not that I expect you'd make any duds.......

Yep ... I am going to experiment a little this summer regards growning duckwwed, alga, azolla etc. etc...but I think duckweed is the go for biggger fish .. crush it in you fingers for the little ones ... and supplement with other stuff maybe ..

I think I am going to use old cat littler trays and buckets ... to grow up all sorts of algae and stuff when we get a little more warmth here in Perth! (So cold right now!)

and the mozzie thing ... in WA ... my daughter got a Mozzie bourne NOTIFIABLE virus when she was little .. She was VERY sick for over a year!

Couldn't even walk!

So a few carnivore fish to take care of the larvae would be a great idea!

Take care folks!

Johnnie