Aquaponics Digest - Fri 01/21/00
Message 1: Ignored requests
from Peggy & Emmett
Message 2: RE: Aquaponics Digest - Thu 01/20/00
from tshandwerker@mail.umes.edu
Message 3: nutrients in fish waste...
from "Marc Laberge"
Message 4: Re: nutrients in fish waste...
from Ronald Polka
Message 5:
from Grant Harper
Message 6: trout densities
from "Marc Laberge"
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Subject: Ignored requests
From: Peggy & Emmett
Date: Fri, 21 Jan 2000 08:49:24 -0500
Hey Bob up there in the cold country, repost your questions. Maybe they
won't be ignored this time. ......Emmett
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Subject: RE: Aquaponics Digest - Thu 01/20/00
From: tshandwerker@mail.umes.edu
Date: Fri, 21 Jan 2000 09:36:13 -0500
One of the major reasons to remove the solids after a time in aquaponics is
the fecal matter begins to product materials that put the fish off feed. If
they do not grow, no money.
Tom
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Subject: nutrients in fish waste...
From: "Marc Laberge"
Date: Fri, 21 Jan 2000 18:48:39 -0500
Hi Tom, I would love to know about what materials are released as the fecal
matter breaks down . ( your reference say aquaponic digest...can you give me
more info on this.)
Hi Donna, don't be ashamed to ask questions; your questions are great and in
no way are they dumb.
With regards to your questions;
1. How long for trout to reach marketable size?
This would all depend on the market your looking at, you can raise
them to fingerlings ( 3" ), to stock outfitters, pond fishing , lakes and
rivers ( all sizes of fish ), or you can raise them to growout sizes for
restaurants and food stores.
The temperature of the water will determine the amount of time it will
take for the fish to grow. ex a 3" trout can reach 13" and weigh almost a
pound in 9 months at 15C ( 60F ).
2. Trout densities.
As I mentioned I am no expert with tilapia; I am not sure if fish
densities are similar. Trout densities vary according to there size. Smaller
fish range around 18kg / meter cube and larger fish up to 55 kg / meter
cube. The rule of thumb is 1.85 kg of fish per meter cube of tank per cm of
fish. ex. a 30 cm fish would be;30x 1.85 = 55.5 kg/m3 .
3. Do catfish thrive in cooler water more than trout...
I would say no, in order of increasing temperature it would be trout,
catfish then tilapia. Temperature is one thing with trout but the other
biggy is oxygen, unlike tilapia or catfish, trout need a lot of O2. It is
not recommended to drop below 65% of saturation of O2 at the exit of your
tanks ponds or whatever.
4. 12-15C....this equals around 55-60F
5. Having not worked with tilapia I could not tell you weather trout is an
easier product than tilapia to market and such. I would imagine that cold
water fish would spoil faster than warmer water fish, making it more
difficult to deal with the trout than the tilapia.
Hope this helped
Marc Laberge
Mont Tremblant
Qc.,Canada
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Subject: Re: nutrients in fish waste...
From: Ronald Polka
Date: Fri, 21 Jan 2000 17:32:50 -0700
Snip
>2. Trout densities.
> As I mentioned I am no expert with tilapia; I am not sure if fish
>densities are similar. Trout densities vary according to there size. Smaller
>fish range around 18kg / meter cube and larger fish up to 55 kg / meter
>cube. The rule of thumb is 1.85 kg of fish per meter cube of tank per cm of
>fish. ex. a 30 cm fish would be;30x 1.85 = 55.5 kg/m3 .
Marc
There is an inherent error in this rule of thumb. Tying the tank biomass
to fish length means that a longer fish increases the stocking density
directly. Your example of a 30 cm fish yields 55.5 kg/m3. This biomass is
at the limit of practical density in a real world situation. If you had 45
cm fish your projected possible biomass would go up to 83 kg/m3 which is
impossible to attain. I don't have any experience with trout, I have grown
tilapia, largemouth bass, and hybrid striped bass. I have found that the
practical limit in an intensive culture system for tilapia is about 50
kg/m3. At this density the fish are stressed from overcrowding. They stop
breeding, which is an advantage for market culture. They are prone to
leaping out of the tanks due to territorial aggression. They have a
tendency to feed less, and the growth rate drops off radically. Simply put,
growing under conditions this crowded reaches a point of diminishing
returns. When crowding causes fish to reduce there intake of feed to a
solely maintenance level than the growth curve flattens out and continued
feeding becomes a waste of money. At that point if larger fish are desired
then it is time to reduce the tank population.
Ron Polka
Southwest Technology Development Institute
New Mexico State University
Box 30001, Dept 3SOL
Las Cruces, NM 88003
rpolka@nmsu.edu
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From: Grant Harper
Date: Fri, 21 Jan 2000 18:14:25 -0800 (PST)
unsubscribe
__________________________________________________
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Talk to your friends online with Yahoo! Messenger.
http://im.yahoo.com
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Subject: trout densities
From: "Marc Laberge"
Date: Fri, 21 Jan 2000 22:00:33 -0500
Hi Ron,
Thanks for the interesting stuff on tilapia I'm learning more about
the fish all the time thanks to people like you. An interesting thing about
trout is , they have 2 types of behavior, individual and schooling behavior.
Individual or dominant behavior occurs when density levels are too low, a
simple thing as a shadow projected on the tank is enough for the fish to
fight for and create a dominant fish.
When you remove the dominant fish, another will soon challenge the other
fish for dominance.
By increasing the density levels of trout, fish soon take a schooling
behavior and dominance is reduced to almost nothing. This is very important
to maintain uniform length of fish . Once dominance is crushed all fish ( in
a perfect tank ) eat equally and fish lengths vary
less. The rule of thumb is not one made up by myself ; it is used in
trout,salmon and charr culture, though modified depending on fish enclosure.
Circular tanks and raceways use 1.85 Kg/m3/cm and ponds use 1.2 kg/m3/cm,
I'm not sure about net pens. These figures are maximum density ones. In
Norway there are recirc units holding arctic charr which run at 80 Kg/ m3
this is because arctic charr are extremely aggressive compared to rainbow
trout , and their growth curve plateaus at I believe 90 then decreases).
It is also worth noting that 50-55 Kg/m3 is considered the maximum densities
to be used for trout I.e. very similar to tilapia. I agree with you 100%
about reaching a point of diminishing return ; once this is reached it's
time too reduce population. As you say stressing fish is not desirable,
farmers working at high densities must have the proper equipment and know
how to use it.
It's very interesting exchanging notes with you Ron thank you.
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