Backyard Aquaponics
A place to discuss aquaponics

Silver Perch (Bidyanus bidyanus), a fish found native in the Murray Darling basin in eastern Australia, and boy they are one tough fish...





I've had Silver Perch in at least one of my systems now for well over 3 years. Some of those perch have been swapped from system to system as I've built new ones and experimented. They've suffered power loses, pea soup water conditions, water temperatures ranging from 13-30, and the ph so high that it's off the scale of my small ph test kit. Conditions that have killed off Black Bream, Baramundi, and Murray Cod in the same system, yet the Silver Perch just keep kicking on.

Silver Perch fingerlings are available in most states of Australia and if your keen to try and grow them, get hold of your local department of fisheries, they should be able to provide you with information on where to get some fingerlings.

tough to kill - my kind of fish

Hi all,

Another bit of info that i've come across regarding silver perch is that they are omnivores, that is they eat insects as well as plant life, and apparently the ratio of the two leans more towards the plant life as they get older.

I forgot to mention that i used to regularly feed mine with baby spinach and lettuce. they love it.

Just tonight i put a hand full of the above scraps into my aquarium with a solitary (small) silver perch and maybe 4 hours later it was all gone!

how cool is that, the green scraps from the veggies you grow go back into feeding the fish that feed your veggies. I reckon thats as closed a loop as you can get.

What a great fish!

Steve

Duck weed doesn't last long in a tank of silver perch, although from what I have read it doesn't contain much in the way of protein, and protein is what really puts the growth into the fish..

Hey Steve...

You want to read about a crazy mixed up closed loop system try following this discussion that was had a while back on the permaculture group.

http://forums.permaculture.org.au/viewtopic.php?t=759

It's a bit long, but woirth a read when you have nothing better to do....

Joel, I can't remember who, but someone who just joined the forum has a website that raves about duck weed....had quite high figures for protein.

Your right Corny, that would be Gary and his website website and I stand corrected. All of the information I have managed to scan on the net just now says that it contains between 30 and 45% protein..

I had heard it from someone on another aquaponics discussion group, the complete opposite, just goes to show you shouldn't always believe what people tell you blindly....

Though I have also just found another source that says protein can be as low as 6%.....

I guess the growth rate would be the best indication.

Thanks Joel,

Will check out that thread when i get a chance.

I've also read that duckweed is high in protien.

I think the confusion arises between DRY weight and WET weight.

I do belive the protein value of dry duckweed is 30% to 40%.
But when you consider that most green veg's are around the 70% water mark then it all makes sense.

the protein content of fresh duck weed would be 40% OF 30% the wet weight.

100grams (which would be a lot of duck weed) times by .3 times by .4

would give you 12 grams of protien. Which when you think about it inrelation to fish with a good feed conversion ratio is not too bad at all!

Mmmmmmmm, maths!

i'll definatly have a connected yet isolated from the fish tank where i can grow some serious duckweed. It wouldn't stand a chance in the main fish area.

Just did another quick calc.

the wet weight protient using my figures (and the 70% water was just ball park) works out to 12% protein.

So i guess both could be considered right if people stated what they meant!

I've researched heaps on the web, and its really amazing how many people will just cut and paste figures onto their web site with out understanding or verifing them.

I was looking up wheat grass once, and i found three websites that had copied the same info. i could tell becasue they all had the same spelling mistake on a particular word

Nice one Steve, makes perfect sense...

With a bit of luck Gary might step in and tell us about his experience with duck weed as well..

Almost everything I know about duckweed, I've learned from the work of scientists who have posted their research results on web.

The article that appears on my website was premised upon (rather than 'cut and pasted') from the work of some Australian researchers based at the University of New England in Armidale. You'll find their details at the end of the article.

On the subject of protein content, here's some of what they had to say:

"Fresh duckweed contains about 92-94% water. Fibre and ash content are higher and protein content is lower in duckweed colonies that grow slowly.

The concentration of nutrients in dry matter of a wild colony of duckweed growing on nutrient-poor water typically is 15 to 25% protein and 15 to 30% fibre.

Duckweed grown under ideal conditions and harvested regularly will have (in dry matter) a fibre content of 5 to 15%, a crude protein content of 35 to 43%, and a polyunsaturated fat content of about 5%, depending on the species involved."

It is apparent from reading what the experts had to say that wide variations in protein content will occur based on the nutrient content of the water in which the duckweed is grown.....and "subject to the species involved."

My own experience of duckweed is limited to some propagation trials to gauge the speed with which the plant breeds up and some observations about its sensitivity to high temperatures.

We plan to build a larger pond in which to grow duckweed as part of our greywater management system. Given its ability to remove nutrients from fish tank water, there's no reason why a duckweed pond shouldn't also be part of any Aquaponics system. The fish benefit from the nutrient removal and they get to eat the duckweed, too

I hope this helps.

Gary,

What have your observations been regarding duckweeds sensitivity to higher temperatures.

What have you found the ideal temp to be, and what would you say the high end temperature would be?

Thanks

Steve

Hi Steve,

Researchers at the Centre for Duckweed Research & Development (UNE Armidale) determined that duckweeds grow between 6 and 33 degrees Celsius. This is consistent with our experience where our plants died off once the water temperature rose consistently over 35 degrees.

In our case, the water temperature probably exceeded the ambient temperature because the black plastic tub in which we grew the plants was in full sun and possibly acted as a solar pond.

Our current container is deeper and is partly buried into the soil and is in semi-shade for at least part of the day. The duckweeds in this container grow quite happily.

Several researchers claim the optimum growing temperature to be in the range of 25 - 32 degrees Celsius. The other thing that they all agree on is that duckweed will not thrive in windy conditions or in fast-flowing water.

Nice one Gary, thanks for the info....

I'm going to look at setting up some duckweed tanks in my next system that I'm designing at the moment.

Thanks