The Development of a Recirculating Culture System for Quahog (Mercenaria mercenaria) |
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With funding from the
SouthEastern Massachusetts Aquaculture Cooperative (
SEMAC
) we are examining alternative methods for the culture of shellfish.
During the past year we have specifically been testing a small-scale,
easy to operate, temperature controlled, recirculating aquaculture system
for rearing quahog seed even at times of the year when growth is normally
slow and mortality is high.
The primary system trial was run with slow growing quahogs provided by the
town of Falmouth that were too small to be field set.
As we would not receive these animals until late October 2002
a preliminary system trial began in April with quahog seed stock (~2mm) from
ARC. This is will be referred
to as Phase I, whereas the primary experiment of culturing of quahog juveniles
(~6-18mm) provided by the town of Falmouth will be referred to as Phase II.
This website is designed to provide the public with a description
of our research. In addition,
we have provided information necessary for others to utilize this technology.
Background
The primary objective of this project
was to support and enhance sustainable growth within the aquaculture industry
by developing an alternative system to be used in the nursery rearing of quahogs.
The proposed system consists of a small-scale, easy to operate, temperature
controlled, recirculating aquaculture system capable of cost effectively rearing
quahog seed even at times of the year when growth is normally slow and mortality
is high. The basic components and technology incorporated into this system
have been used successfully to culture a variety of aquatic species, but
to our knowledge they have never been applied to shellfish culture. By utilizing
this technology to rear quahog seed, the hypothesis was that growers would
potentially be able to accomplish two important goals:
1) Because of the
elevated temperatures in the recirculating system, seed will growth at a
faster rate than seed reared in ambient water (especially during the early
spring and late fall)
2) Growers could
over-winter their sub-field plant size seed in a temperature-controlled
environment, thus avoiding the typical 80-90% “winter-kill” mortality rate.
Overall, the technology developed
by this project will contribute to the advancement of the aquaculture industry
in southeastern Massachusetts by possibly allowing quahog seed producers and
grow-out facilities to get a higher percentage of their product to a marketable
size. Furthermore, the simplicity of the system in conjunction with the release
of this informational could significantly increase the number of growers
capable of maintaining and growing seed stock – this could substantially increase
the overall quantity of quahog seed available for re-seeding waters of the
Commonwealth.
Phase I
Week starting ... Status of the project
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April 21 |
System is assembled at the Marine Resources Center. |
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April 28 |
Flow is modified to facilitate the autonomous removal of waste debris. System is operating with seawater. |
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June 3 |
Upwellers constructed (see link below ) |
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June 10 |
Quahog spat received, two upwelling nursery systems running. |
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June 24 |
Regular feeding and husbandry began |
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July 1 |
Algal Paste diet double to approx. 40 mls/day, two feedings a day |
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July 8 |
Debris in upweller system increased and was flushed with moderate water pressure |
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July 15 |
Adding approximately 14 gallons of water each week due to evaporation |
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July 22 |
Quahogs at Green Pond at 9mm compared to 3.5mm at MRC |
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July 29 |
Water temperature increased to ~25. Flow reversed and decreased during feeding. |
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August 18 |
Growth rates significantly lower at MRC compared
with Green Pond. |
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September 23 |
Fish Farm drained and cleaned. Both upwellers now in 55 gallon trash cans with flow through seawater. |
Photos
Week of June 10
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Week of August 18
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Water quality data was taken throughout Phase I and
can be seen in the graph below.
Phase II
Last November, Paul Montegue (Falmouth Shellfish Officer) provided us with
approximately 35,000 quahogs from two separate pump driven upwellers located
at Green Pond and in West Falmouth. The quahog juveniles ranged in size
from 6-18 mm and were divided among 4 upwellers
. We cultured the juvenile quahogs in the upwellers for 20 weeks in
room temperature seawater. They were fed a diet of marine microalgae
concentrate (Instant-Algae, Reed Mariculture). Though there are reports
that live algae can generate high grow rates, the culture of live algae is
very labor intensive, requires considerable space, energy and expertise, and
is usually the key factor preventing the successful culture of shellfish.
Thus, we felt it important to investigate the use of prepackaged algal paste.
Each day the quahogs were fed approximately 37 mls of
microalgae concentrate which was equivalent to feeding 2% of the total wet
tissue weight in dry algae. The algae diet was a 1:1 mix of Tetraselmis
and Isochrysis at a total cost of $336.00 (US) over the entire
period. A small subsample of juvenile quahogs can be seen feeding in figure
4. Throughout the 20 weeks that quahog were held in the system, salinity,
pH, ammonia, nitrite and nitrate all remained within acceptable levels.
During week 10, nitrite levels did begin to rise above baseline and
supplemental biofiltration was added by suspending a 0.4 cubic meter bag of
Bio-Fill ™ media in the tank. Excess feces and detritus were siphoned every
5 weeks and dechlorinated fresh water was added periodically to replace evaporative
loss.
Photos
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Conclusions
Following acceptance of our Final Report to SEMAC we will provide additional
information related to Phase II such as water quality data, results, and opinions
on the feasibility of such a system.
Please check back to see additional information.
Please direct questions and comments related to this project to:
Marine Biological Laboratory
7 MBL St
Woods Hole, MA 02543
phone 508.289.7683
fax 508.289.7900
Links
Diagram and instructions for constructing upwelling nursery system (PDF format)
