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Isolation of Australian microalgae and preparation of microalgal concentrates for use as aquaculture feeds

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Knuckey, RMP (1998) Isolation of Australian microalgae and preparation of microalgal concentrates for use as aquaculture feeds. PhD thesis, University of Tasmania.

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Abstract

In this study, two types of microalgal feed were examined; 1) algal concentrates and 2)
new Australian microalgae. Algal concentrates were examined because for
aquaculturists, they could provide an off-the-shelf alternative to maintaining live algal
cultures. Australian microalgae were examined to identify new feed species and to
determine specific dietary requirements of local juvenile Pacific oysters (Crassostrea
gigas).
Ten diatoms, microalgae widely cultivated as feed for aquaculture species, were isolated
and purified from local waters, Tasmania, Australia. Proximate analysis of logarithmic
and stationary phase cultures showed major differences between species and in the
effect of stationary phase on composition. Four species (Attheya septentrionalis,
Entomoneis cf. punctulata, Extubocellulus spinifera and Thalassiosira oceanica) were
evaluated as feed for juvenile Pacific oysters. Fed as the major component in a ternary
algal diet, two algae (Attheya septentrionalis and Entomoneis cf. punctulata) supported
over 80% of the growth of the T. pseudonana control.
Centrifugation of eleven microalgae from a range of classes showed it to be an efficient
(>80 % recovery) way to concentrate microalgae. Small chlorophytes survived the high
shear forces best but, are documented poor algal diets for oysters. Of the diatoms
Chaetoceros calcitrans and Thalassiosira pseudonana were least damaged. Juvenile
oyster feeding trials showed that T. pseudonana pastes were capable of sustaining
limited growth. However, nutritional deficiencies in the pastes were reflected in falling
weekly growth rates, by the third week, oysters grew only marginally or lost organic
weight.
An alternative, low shear concentration process was developed based on chemical
induced flocculation. Initial coagulation of algae was induced using Fe +3 or by
increasing pH. Flocculated concentrates of T pseudonana were fed to juvenile Pacific
oysters and compared to live T. pseudonana and centrifuged algal pastes. The pH flocculated algal diet was superior to all other test diets and lost nutritional value more
slowly than centrifuged algal diets.
In the discussion the nutritional composition of algal diets is related to the composition
and nutritional requirements of the juvenile oysters. It is argued that the dietary protein
content of live algal diets, not limited in essential nutrients, is the most significant factor
in determining a nutritionally superior diet. The nutritional value of algal concentrates
is discussed and flocculation is concluded to be a superior method to produce
concentrates. It is shown that flocculation is applicable for concentrating many algal
species and argued that it is a cost-effective process with commercial applications.

Item Type: Thesis (PhD)
Keywords: Crassostrea, Marine algae
Copyright Holders: The Author
Copyright Information:

Copyright 1998 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:

Thesis (PhD. )--University of Tasmania, 1999. Includes bibliographical references

Date Deposited: 19 Dec 2014 02:40
Last Modified: 06 Sep 2017 04:45
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