From: Randy Reed <rreed@seafarm.com>
Reply-To: AQUA-L@LISTSERV.ifmt.nf.ca
INCREASING OYSTER GROWTH
QUESTION:
I am conducting an experiment with European (edulis) oysters to see how rapidly they can be made to grow. They are being fed exclusively on Chaetoceros at a saturation of 8000 / ml. When I open the oysters up they have an obviously distended gut filled with the microalgae, but they don't seem to be digesting it very rapidly or growing very fast. Does anyone have suggestions on what I can do or change to make them grow more rapidly?
Randy Reed
CEO, Reed Mariculture, Inc.
e-mail rreed@seafarm.com
web http://www.seafarm.com
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COMMENTS 1:
Two comments:
1 - 8000/ml (assuming you are talking cell counts) is extremely low as a feeding concentration. I shoot for 25,000 up and for older animals I try to maintain a considerably higher density.
2 - a diet of exclusively one species will not give you as good growth
as a mixed diet. I combine Chaetoceros with Isochrysis. Many other
combinations work well and if you can feed three or more types that is even better.
Nancy Hadley
MRRI
PO Box 12559
Charleston SC 29422-2559
hadleyn@mrd.dnr.state.sc.us
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COMMENTS 2:
I agree with Nancy you would do better to put the cell density up and
increase your diversity of species, Chaetoceros and Iso are good,
maybe also go for some larger green's such as Tetraselmis spp and
Dunaliella. A small proportion of sediment (such as diatomaceous
earth and fine sediments) in the diet may also help (probably
increases digestability by breaking up algal cell walls but may also
contribute C to diet).
Keep the water moving well and aeration adequate.
sam
sam@environment.cawthron.org.nz
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COMMENTS 3:
8000 Cells/ml isn't near enough for adult O. edulis, or any other
species of oyster I know of. It isn't even enough for larvae. We start
larvae at 30K cells/ml, then step it up to 50K, then 80K, then 100K around settlement time. Depending on oyster densities, spat can usually take down 100-200 cells/ml with no problem. Temperature of course plays a role; we grow larvae at 23-28 degrees C, depending on various factors: sometimes we want to slow them down to study metabolic and other processes in which case it's around 23; other times we just want to move them thru, in which case it's 26-28.
I think that in general oysters, especially spat and adults, do better on
a varied diet...either mixed cultured algae or, best of all, wild
phytoplankton. 8000 cells/ml might be viewed as a subsistence diet, but I think it takes at least 10 times that to get good growth.
Will Borgeson
<wdborgeson@ucdavis.edu>
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COMMENTS 4:
I would begin feeding a multi-species diet (One of many examples:
T-iso/C-iso/OR Va-12; Chaetoceros; and Tetraselmis/or Dunaliella).
What size are the oysters you are working with? How many oysters
per tank? 8,000 c/ml (per day?) seems very low. Off the
top of my head:
My adult broodstock oysters get somewhere around 3.1 billion c/ml/oyster/day...
Setting animals (approx. 212 microns) get somewhere around
500K to 3 million c/ml/system/day...anywhere from 100,000 to
10 million setting oysters per system.
Larvae (35 microns--180 microns) get anywhere around 35,000 to
80,000 c/ml/tank/day...really rough that works out to approx. 22,000 cells/oyster larvae/day.
Have you noticed pseudofecal output? If so you may want to change how you are feeding your oysters--i.e. continuous vs. batch feeding...
Do your oysters have any signs of sickness?
Are other tank parameters optimal? (i.e. aeration, water temp., etc.)
P.S. Depending on your Chaetoceros spp. you may want to aerate your Chaetoceros vigorously (to help break the spines) before feeding it to your oysters...I have seen this to be helpful with oyster larvae.
Kim Simmons
VIMS Aquaculture Center
The College of William & Mary
P.O. Box 1346
Gloucester Point, VA 23062
U.S.A.
Phone: (804) 684-7301
FAX: (804) 684-7045* (not private)
*Person's Name & Building Name Must Be On FAX
e-mail: ksimmons@vims.edu
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