[Sc-aquaponics] Feeds and Duckweed

[Dr. Dave Smith]

Charlie is also correct, and it also relates to the low quality and
digestibility of duckweed protein.  People have been culturing duckweed for
animal feed for a long time (see Dudley Culley's work in the 1970's in
Mississippi and Louisiana), but this was for ruminant cattle feed.  It is
probably only suitable for herbivorous fish like white amur (grass carp).
As a matter of fact we often feed our goldfish a higher protein (38-42%)
small-sized pellet, and feed conversions are good because they need so
little of it.
---Dr. Dave


On Thu, Jan 23, 2014 at 12:11 PM, Charlie Shultz <aquaponics at hotmail.com>wrote:

> I'll add a couple comments on the Duckweed.  You will read online that
> Duckweed is a good feed for fish.  It can be, but it's certainly not a
> complete diet.  There are a couple main strains, and they average about
> 30-40% Protein which is great, eh!  The problem is Duckweed is about 95%
> wet weight.  To feed the fish effectively you need to dry the duckweed.  It
> will take a lot of wet duckweed to produce the required food in terms of
> dry weight.
>
> Since you are in a school setting though you can experiment.  Maybe you
> can have the kids repeat a trial I once did with a college student:
>
> I set up a small recirc system and stocked Nile tilapia.  The student
> weighed the biomass that we started with.  For 30 days the student fed
> Duckweed only to the tilapia, 3x daily for 30 minutes each feeding.  Any
> excess duckweed after each 30 min feeding was removed from the tank.  After
> 30 days the student weighed the fish and was shocked to find they lost
> weight during that period.  She was crushed with her results as she
> expected them to grow much better.  The take home message was important
> though.  It seems the tilapia would fill up on the diets that were
> primarily water.  Before gaining the nutrition they required they were full
> on wet Duckweed.
>
> On a small-scale, growing and DRYING Duckweed may be a potential
> alternative ingredient for fish like tilapia, but I would still provide a
> variety of ingredients for healty animals.  On a large commercial scale,
> farming-harvesting-drying duckweed will become a labor and energy intensive
> operation.
>
> Would love to hear if you do play around with duckweed and what kind of
> results you find.
>
> Charlie Shultz
> Lethbridge College
> Alberta
>
>
> > What kind/brand of food source would you recommend for comet goldfish
> and shubunkins in a 275-gallon IBC aquaponics system? Most of our 18 fish
> are between 4-6" in length.
> >
> > Has anyone grown duckweed as their primary (or exclusive?) food source
> for their fish in an aquaponics system?
> >
> > I've read online about the use of duckweed, but I'm really wanting to
> learn more from those who might have done this.
> >
> > Thanks for any insight you can offer.
> >
> > Jeff Bracken
> > bracken5 at columbus.rr.com
> > Chemistry Teacher
> > Westerville North HS
> > Westerville, Ohio
> >
>
> _______________________________________________
> Sc-aquaponics mailing list
> Sc-aquaponics at lists.service.ohio-state.edu
> https://lists.service.ohio-state.edu/mailman/listinfo/sc-aquaponics
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osu.edu/pipermail/sc-aquaponics/attachments/20140123/0cbe5af4/attachment.html>