Aquaponics Digest - Thu 02/05/98
Message 1: algal nutrition for tilapia
from james.rakocy@uvi.edu (James Rakocy, Ph.D.)
Message 2: Re: algal nutrition for tilapia
from "H.Doelle"
Message 3: Re: intro
from Chad Kruger
Message 4: Re: response to animal-waste aquaculture
from Jack Rowe
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Subject: algal nutrition for tilapia
From: james.rakocy@uvi.edu (James Rakocy, Ph.D.)
Date: Thu, 5 Feb 1998 15:54:12 -0400 (AST)
Hello Everyone, I was just looking at some of our data and I've been doing a
lit. review concerning mamured and/or fertilized ponds as well as fed ponds.
You might find the results interesting. In our greenwater recirculating
system (clarification only) that was choked with algae, including periphyton
(attached algae) and dead algae in a 1.4 m3 clarifier with only 15 male Nile
tilapia in it, the clarifier tilapia grew at a rate of 0.48 g/day (initial
weight was 71 g) while the open tank fish (28.6 m3 tank volume) stocked at
26 fish/m3 which received ample floating pelleted feed (32% protein) grew at
a rate of 2.64 g/day, same initial weight. The clarifier fish did not get
pellets. The data (courtesy of Bill Cole) was based on three replications.
So it seems that feeding to satiation with algae in this system produces
only 18% of the growth rate that can be achieved with a concentrated dry
(91.1% dry matter) feed pellet. With algae, fish eat a lot of water which
must be voided, which cuts their daily dry matter intake and requires energy.
Now in ponds with manure and/or fertilizer, the best growth rates for male
Nile tilapia are about 1 g/day, often less. The fish are usually stocked at
1-3 fish/m3. Studies show that the main value of the manure is for the
inorganic nutrients it releases for algal growth. With feed or feed and
fertilizer the growth rate will go up to about 3 g/day, but sometimes much
less. This is a vast simplification that not does not consider many factors
such as water quality. But here again the algae-based system only produces
about 33% of the growth rate obtained with feed. The densities were much
lower than the greenwater tanks but there was no supplemental areation to
improve water quality as in the heavily stocked greenwater tanks.
Now in our aquaponic tanks just a couple weeks ago we achieved an average
growth rate for male red tilapia of 3.7 g/day at a stocking rate of 143
fish/m3, but the water quality was excellent, no pure oxygen though. In the
past with male Nile tilapia at 89 fish/m3 in an aquaponic system, we
obtained growth rates of 4.9 g/day.
What does this all mean? It means that algae is a fine food for tilapia if
it comes free or at low cost and you can live with low growth rates. If,
however, you are paying dearly for heating, aeration and pumping, have a
limited amount of space, and would like to recoup some of your output by
selling the fish, you better stick with concentrated fish feeds and forget
the algae. I'm braced for the critiques. Jim Rakocy
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Subject: Re: algal nutrition for tilapia
From: "H.Doelle"
Date: Fri, 06 Feb 1998 08:47:15 +1100
Dear James,
Very interesting results indeed. However, I think you make too rush a
judgement in regard to algae feeding. I have a couple of comments:
1. you mention the requirement mainly for inorganic nutrients instead of
organics in feeding your fish. This is why the use of diluted effluent from
biodigesters is such a good source. It has been shown that the 30-40%
residual BOD in the effluent can be further reduced by oxygenating the pond
in which the effluent flows either by aeration and/or by algae and the
effluent from that pond is excellent source for fish production. At that
stage the organics are low, but the inorganics are still high.
2. I would be careful with comparing algal feed with the artificial feed you
can buy. Are you 100% sure that there are no antibiotics, hormones and/or
other stimulants in it ? I found some of them a few years ago in an Asian
feed. If you do the system under point 1, you have the algae very cheap, as
you produce it yourself.
I also have seen in Mexico, that they produce fish with the algae in the
same pond, as the algae oxygenate the pond, but I am not sure whether it is
enough oxygen.
If you use the shallow pond with algae between the anaerobic digester tank
and the deeper fish pond, the feed from the shallow pond is oxygenated
through the algae.
3. I think, although I am not an experienced aquaponist as yet, the fish
response to feed is a little more complicated than you state it. Surely you
must also have great expense for the commercial feed.
I thought you may be interested in a different aspect of thought.
Best wishes
Horst Doelle
At 03:54 PM 05/02/98 -0400, you wrote:
>Hello Everyone, I was just looking at some of our data and I've been doing a
>lit. review concerning mamured and/or fertilized ponds as well as fed ponds.
>You might find the results interesting. In our greenwater recirculating
>system (clarification only) that was choked with algae, including periphyton
>(attached algae) and dead algae in a 1.4 m3 clarifier with only 15 male Nile
>tilapia in it, the clarifier tilapia grew at a rate of 0.48 g/day (initial
>weight was 71 g) while the open tank fish (28.6 m3 tank volume) stocked at
>26 fish/m3 which received ample floating pelleted feed (32% protein) grew at
>a rate of 2.64 g/day, same initial weight. The clarifier fish did not get
>pellets. The data (courtesy of Bill Cole) was based on three replications.
>So it seems that feeding to satiation with algae in this system produces
>only 18% of the growth rate that can be achieved with a concentrated dry
>(91.1% dry matter) feed pellet. With algae, fish eat a lot of water which
>must be voided, which cuts their daily dry matter intake and requires energy.
>
>Now in ponds with manure and/or fertilizer, the best growth rates for male
>Nile tilapia are about 1 g/day, often less. The fish are usually stocked at
>1-3 fish/m3. Studies show that the main value of the manure is for the
>inorganic nutrients it releases for algal growth. With feed or feed and
>fertilizer the growth rate will go up to about 3 g/day, but sometimes much
>less. This is a vast simplification that not does not consider many factors
>such as water quality. But here again the algae-based system only produces
>about 33% of the growth rate obtained with feed. The densities were much
>lower than the greenwater tanks but there was no supplemental areation to
>improve water quality as in the heavily stocked greenwater tanks.
>
>Now in our aquaponic tanks just a couple weeks ago we achieved an average
>growth rate for male red tilapia of 3.7 g/day at a stocking rate of 143
>fish/m3, but the water quality was excellent, no pure oxygen though. In the
>past with male Nile tilapia at 89 fish/m3 in an aquaponic system, we
>obtained growth rates of 4.9 g/day.
>
>What does this all mean? It means that algae is a fine food for tilapia if
>it comes free or at low cost and you can live with low growth rates. If,
>however, you are paying dearly for heating, aeration and pumping, have a
>limited amount of space, and would like to recoup some of your output by
>selling the fish, you better stick with concentrated fish feeds and forget
>the algae. I'm braced for the critiques. Jim Rakocy
>
>
>
Horst W.Doelle,D.Sc.
Director, MIRCEN-Biotechnology Brisbane
Chairman, IOBB
Hon.Member of Depts. Microbiology & Chemical Engineering
FAX: +617-38783230
Email: H.Doelle@mailbox.uq.edu.au
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Subject: Re: intro
From: Chad Kruger
Date: Thu, 05 Feb 1998 16:26:10 -0800
Paula,
S & S Aqua Farm wrote:
> At 09:50 AM 2/4/98 +0000, Frank Greenslade wrote:
>
>
> >I do however have a small NFT hydroponic setup in which I am
> >attempting to grow a type of courgette/zuchini known as "sunburst
> >squash" or "scallopini" for our local markets. This is my first
> >season and I have had some problems and successes.
>
> >If there is anyone out there who has grown zucchini in an NFT system I
> >would love to hear from them.
>
> Frank - what type of space requirement does this variety have? A few years
> ago I grew some gourmet yellow squash (can't remember the variety at this
> point, but I could look it up), with some success in our system. The only
> problem I had was allowing sufficient room for the plant. This is what
> happens when you have NO experience with a type of plant, either indoors or
> out, but try it anyway. If I had asked even one of our friends who market
> garden, I'd have had a better idea what to expect, and I think would have
> had more success. Production went well until I had the plants so crowded
> that air couldn't move around them.
>
> Hope we hear from others on various crops. Glad to have you with us.
>
> Paula Speraneo
>
Have you considered utilizing a trellise system to grow your melons or squash.
I don't know if it will work very well in your system, but it is great in our
gardens. We "suspend" all of our melons in the air using nylon stockings. It
allows more space for more plants, keeps down disease and rot problems, and
makes the melons and squash perfectly shaped (more marketable). The other
thing we do when we have space considerations for any type of vine crop is that
we grow them on the edge of our growing area, and let the foliage and the fruit
spill over the edge, providing more room in the growing area for roots. These
are some of the "intensive" tricks we use in our "ecointensive" technologies.
Chad Kruger
p.s. I entered our greenhouse this morning to see our 325 Tilapia floating on
the top of our tank. The thermostat on our hot water tank never turned off
last night. So we have poached fish. Oh well, at least it wasn't our dinner.
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Subject: Re: response to animal-waste aquaculture
From: Jack Rowe
Date: Fri, 6 Feb 1998 00:33:12 -0500
What a lively discussion of late!
Aquaponics is definitely a manure-based system, we just don't have to loo=
k
at or handle the fish's manure (hurray for small favors!). I would mentio=
n
urine also, which is happily more-or-less sterile and so hasn't entered
this discussion. Waste-based, however, aquaponics is (food is of course a=
precursor to all manures). Bergheim et al, in Pillay, 1992 (Aquaculture a=
nd
the Environment), report that "pollution from 1 kg of trout is equal to
that of 0.2 - 0.5 persons". If plants in aquaponics systems were being
fertilized directly with biodegraded excess food particles, not only woul=
d
high BOD (biochemical oxygen demand) of degradation organisms
significanltly lower O2 levels, but one would be overfeeding and so wasti=
ng
relatively-expensive fish food. =
Algal blooms, essential and fundamental to natural pond ecosystem food
webs, are not uniformly bad. A healthy freshwater bloom leaves fingers ju=
st
visible when the arm is submerged to the elbow (FAO Training Series #24,
Handbook on Small-Scale Freshwater Fish Farming). When an algal bloom hid=
es
your fingers, the algal bloom is excessive and results in low dissolved O=
2.
Red tide is not, I think (?) a freshwater phenomenon. =
Salmonella, E. coli, et al in fish probably relates more to hygiene than
meat contamination in the strictest sense. Pillay reports feacal
microorganisms in alimentary canals of fish, but none in musculature or
other viscera (Allen et al 1979). A question remains, especially in
'underdeveloped' countries: is there water clean enough to wash the fish
without further contamination? Are people educated about thorough cooking=
for salmonella, etc?
Dr. Doelle's suggestion of manure fermentation in methane-producing
anaerobic digesters to remove pathogens is a solid one. The resulting
effluent, in addition to being far safer than the original materials, has=
lost none of its fertilizing capacity since the digestion process works
mainly on carbohydrates. And the methane is a bonus not detracting from t=
he
value of the remaining materials. However, the technology may be beyond t=
he
reach of many in poor countries because of cost or lack of information,
tools, etc. And of course there is the very powerful "We've always done i=
t
this way". Such systems in developed countries, a la John Todd's "Living
Machines", are quite feasible.
I think, however, that the answer to the question of using fresh manures =
in
fish production requires looking honestly at which of two complementary
aspects of the issue we are actually asking about. One (theoretical) aspe=
ct
is: CAN it be done safely? The other aspect, on a practical level and muc=
h
more to the point, is: IS it done safely? Often, the answer is 'no'. Huet=
,
in Handbook of Fish Culture, p. 329, shows human latrines in Indonesia
placed directly over fish ponds, a long-time practice in much of Asia. It=
's
doubtful that these latrines are removed from service when algal blooms
have reached maximum usefulness, or when some of the human users of the
latrines are sick. Asian systems also use Carp, which survive in water
which would kill catfish, tilapia and in fact about any European or
American fish.
I think human and animal wastes MUST be used productively in the long ter=
m.
If not, they continue to be pollutants (on a massive scale)... if used
productively and safely they become a resource. Practices of the past wil=
l
often need to be redesigned to accommodate better understanding of
pathogens, etc., but still have value as models. =
Jack Rowe
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