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Intensive production of Artemia franciscana cysts in outdoor ponds

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Tyler, J P (1996) Intensive production of Artemia franciscana cysts in outdoor ponds. PhD thesis, University of Tasmania.

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Abstract

Despite an identified need world wide for reliable supplies of high quality Artemia
cysts for aquaculture, the commercial supply of cysts remains exclusively sourced
from unreliable and low productivity extensive systems producing cysts of variable
quality. An intensive cyst production system for producing high quality cysts in
large outdoor ponds was developed and tested at a commercial saltfield in the
North West of Western Australia. To assist in the development of this system
numerous experiments were conducted to optimise algal production, identify food
requirements of Artemia, and spare algal inputs through the use of wheat po/lard.
In addition, management strategies were assessed for reducing intraspecific
competition in order to increase cyst output.
Culture conditions for three species of naturally occurring brine microalgae
(fetraselmis suecica, Dunaliella viridis and Dunaliella salina suitable as food for
Artemia franciscana, were investigated (Chapter 3). T.suecica grew fastest in
seawater (density 1.025 glmL) and was completely inhibited in concentrated
brines which are optimal for A.franciscana culture (>1.10 glmL, Chapter 6).
D.salina grew best at brine densities >1.10 glmL (Chapter 3.3) and D.viridis in less
dense brine (<1.10 glmL). A concentration of 0.01 g/L of soluble fertiliser was
found to be sufficient for both Dunaliella species in outdoor culture. T.suecica had
lower productivity (cellslmUday) than the two Dunaliella species by about two
orders of magnitude. Four brands of commercially available soluble fertilisers were
tested and found to be similar in their effects on microalgal productivity. The
optimum physical requirements of both species of Dunaliella were similar.
Vigorous aeration and peak light intensities above 7, OOO lux at noon were found to
be necessary to sustain these cultures. Peak D.viridis populations (>3 million cells
per ml) with a sustainable daily harvest rate >40% of culture volume were
achieved. The major problem encountered with outdoor Dunaliella culture was
grazing pressure from contaminating A.franciscana and the brine ciliate Fabrea
salina. The most effective control procedure for these organisms was found to be;
initial sterilisation of culture brine with at least 10 ppm of active chlorine,
inoculation with zooplankton-free microalgae culture, continuous screening for
A.franciscana, and maintenance of optimal conditions for microalgae culture. This
brine often contained F.salina which would quickly denude a microalgae pond if
allowed to colonise that pond. However, if the brine was added to the
A. franciscana pond first, the brine shrimp would effectively eliminate the ciliates
before they reached the algal pond. The growth responses and conversion efficiencies (dry weight food/dry weight
Artemia), of both solitary and communal A.franciscana, for various amounts of
D.viridis and D.salina, were determined in laboratory experiments (Chapter 4.1).
Food level had a marked effect on both growth rates and efficiency at all stages
from lnstar 1 through to lnstar 16 adults. A minimum of between 200,000 and
500,000 Dunaliella cells per animal per day (0.014 g - 0.035 g dry weight) was
required for long term survival of A.franciscana and one million cells per day to
enable development through to lnstar 16. Maximum growth rate was achieved
with four million cells per animal per day. Growth efficiency decreased with
increased feeding level. A feeding rate of between one million and two million cells
per animal per day was considered to be an appropriate balance between growth
and efficiency enabling full animal development with growth efficiency of about
25%. Under highly competitive conditions with uncontrolled A.franciscana
population growth, the population stabilised at a level where each individual
received about 500, OOO cells per day.
Microalgal cultures are relatively dilute on a dry matter basis, however, this is not a
limitation with inputs of dry feeds. Finely ground wheat po/lard flour supplemented
with some D.salina culture was an adequate food for laboratory cultured
A.franciscana (Chapter 4.2). Apparent growth efficiencies for wheat po/lard were
only about 5% of those achieved with a D.salina diet but it was relatively
inexpensive. Pollard on its own was also found to be a suitable food for
A.franciscana in 1,000 L outdoor tanks, however, supplementation with D.salina
(5% of the total food on a dry weight basis) greatly enhanced the biomass of
A.franciscana compared to treatments without supplementation.
Cyst production relies not just on biomass but on reproductive output and
specifically on Artemia adopting an oviparous reproductive strategy. A minimum
food ration of two million D.salina cells per individual A.franciscana per day was
required for high reproductive output. This was difficult to sustain in a communal
population due to population increase and resultant increase in intraspecific
competition. A number of strategies to limit population expansion were trialed.
Selective screening was the one practical technique that was effective in limiting
population expansion and maximising reproductive output at a peak of about 25
offspring per female per three day reproductive period. A mesh size of 1 mm or
smaller was required to retain physically small broodstock (<1 cm length) in a
system with high flow rates. A screen size as large as 2 mm would retain larger
adults (>1 cm length) ifthe flow rates were very low (<500 Um2
/hour).
The variety of factors that could conceivably affect the mode of reproduction were
investigated (Chapter 5). Laboratory cultured animals tended to be ovoviviparous
and animals in outdoor culture oviparous but the switching mechanism was not
identified despite extensive experimentation. Food level, salinity, salinity-shock,
light intensity and oxygen stress in the presence of iron were all tested and no
clear patterns emerged in either laboratory or outdoor trials. Reproductive mode in
the 0. 08 ha experimental pond was primarily oviparous. The above data were used to design an operational large-scale facility for the
production of A.franciscana cysts (Chapter 6). Major practical problems
encountered in the development of this facility included unreliability of electrical
equipment in a saltfield environment, inadequate sealing of screens separating
the D.salina pond from the A.franciscana pond and, sustaining the population of
D.salina for long periods. These problems were all largely overcome and cyst
production levels in excess of 1 kg per day were achieved from a 0. 08 ha pond for
several weeks.

Item Type: Thesis (PhD)
Keywords: Artemia, Shrimp culture
Copyright Holders: The Author
Copyright Information:

Copyright 1996 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Includes bibliographical references (leaves 183-194). Thesis (Ph.D.)--University of Tasmania at Launceston, 1996

Date Deposited: 04 Feb 2015 23:23
Last Modified: 11 Mar 2016 05:55
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