Duckweed Harvest

[GaryD]

Hi,

We freeze duckweed for later use by our Jade Perch. In the past, we've tended to use small plastic tubs and trays as moulds....creating small biscuits of duckweed.

We discovered that getting the frozen duckweed out of the moulds was frequently problematic so we've begun to use larger trays with sloping sides......we end up with one large "biscuit" which is easy to get out of the mould.

A couple of light taps with a hammer and the entire slab of duckweed is coverted to managable chunks of frozen fast food for fish.

GaryD

[DuncanC]

Hey Gary,

It looks like frozen chopped spinach I bet the fish love it! It's great to see options like these for fish feeding when away. It also looks like it would be a lot easier for a family member or temporary system keepr to just throw a 'chunk' in for the fish that possibly measuring fish food out and mixing in soy beans etc.

Cheers,

Duncan.

[GaryD]

Hi Duncan,

Frozen, chopped spinach or silver beet would also be a good greenfeed for omnivores.

Gary

[kenc45]

In the May Issue of the Practical Aquaponics Newsletter says that duckweed dies off at temps above 30 deg. Is this water temp, or air temp? Basically, I'm asking if I'd be able to grow it- as air temp up here is over 30 most days.

[GaryD]

Hi Ken,

I wrote that article and it refers to water temperatures.

There are many species of duckweed.....some of which are native to warm places. There's a nice little species called Wolffia that comes from around Cairns and that should be perfect for your purposes.

When you go to Darwin, do the rounds of the aquarium places and you're bound to find some local duckweed.

Gary

[gtpratt]

I am wondering if we have duck weed in our pond?

We bought a small bit of Azolla? from the local garden centre and it quickly grew to become a mat of large thick green stuff on the top of the pond. In winter it went red and is now starting to go green again?

Does this sound like the duck weed you guys refer to or is it something else?

Should I be harvesting this and attempting to keep the plants small.

I note the chooks dont seem to go wild trying to eat it.

I also have a problem of some kind of noxious weed in the pond I will be removing this and attempting to let the azolla take it over.

Any advice gratefully received.

Gra.

[GaryD]

Hi Graham,

Azolla and duckweed are two quite different plants.

The duckweed we have is tiny.....probably about 2mm in diameter.

Gary

[gtpratt]

Hi Graham,

Azolla and duckweed are two quite different plants.

The duckweed we have is tiny.....probably about 2mm in diameter.

Gary

Clearly I do not have duck weed.... Where can I get some? anybody wanna send me a cotton ball with water and a little duck weed on in a plastic bag?

Naturally I will ensure that the grow pond for the duck weed does not have external access for birds etc.

Kindest regards.

Gra.

[GaryD]

Hi,

A duckweed tank is an integral feature of our new 4 tank set up.

We used a 585 litre grow bed for the tank. It is connected to a 950 litre fish tank containing about fifty 75mm-100mm Jade perch fingerlings.

Bio-filtration is provided by a 235 litre grow bed filled with clay pebbles. Duckweed also assists with the maintenance of water quality in that, not only does it remove nitrates from the water, it will (unlike other plants) use ammonia in its un-ionised form.

A simple weir arrangement ensures that the water level in the duckweed tank remains constant and a bypass line on the pipework from the fish tank to the bio-filter ensures a slow, steady flow of nutrient rich water into the duckweed tank.

I've mounted a mini-greenhouse cover on the tank and this creates the hot and humid conditions favoured by the species of duckweed that we grow.

Photo 1 - the duckweed tank
Photo 2 - the weir arrangement that maintains the tank level. If we used the usual standpiple set up to maintain water level the duckweed would be sucked into the tank. The weir keeps the duckweed in the tank while allowing the water to return to the fish tank.
Photo 3 - fast food for fish.

Gary

[Dufflight]

The stuff I borrowed out of the local lagoon does not look like that. Will take a close up photo later and post the pic. Fish still eat it.