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The identification and development of probionts for use in marine fish hatcheries

De'Pannone, MV 2010 , 'The identification and development of probionts for use in marine fish hatcheries', Research Master thesis, University of Tasmania.

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Striped trumpeter (Latris lineata) is currently being researched as a new
candidate for the Tasmanian aquaculture industry. Larval development is
protracted and unusual in the striped trumpeter, and successful mass culture
has taken over 15 years. Recent breakthroughs have been made in the
successful culture of seedstock, including the use of ozonated water to
reduce and control microbial communities. The subject of this thesis was the
implementation of research to further improve larval and juvenile rearing
success through the use of bacterial probionts.
A knowledge of the microbial bacterial community of the larvae, seawater
and live feeds was necessary in order to develop an understanding of what
represents a healthy microbial ecology relevant for larval fish rearing
success. 16S ribosomal RNA (rRNA) gene-based clone library and terminal
restriction fragment length polymorphism (TRFLP) analyses were utilized to
examine the microbial community associated with larvae cultured under
different "greenwater" conditions. It was discovered that the larvae-associated
microbial diversity was restricted but varied considerably between
culture conditions. Most bacteria detected on the basis of cloned16S rRNA
gene sequence data, belonged to class Alphaproteobacteria (predominantly
of the Roseobacter clade), Gammaproteobacteria (genus Psychrobacter and
Pseudoalteromonas) and Actinobacteria (genus Microbacterium). No
association was found between larval survival and microbial community
structure. Using TRFLP analysis, similar results were obtained and
demonstrated that the bacterial composition was in agreement with the clone library data. It was found that the microbial community in the larvae was
distinct from the bacterial community present in the surrounding water.
Potential probiotic candidates were identified using antimicrobial in vitro plate
testing against known pathogenic Vibrio species, with six out of 25 isolates
tested selected for further testing. The 25 test bacteria were obtained in a
previous experiment and were determined to be a representation of the
bacterial community present in 15 days post-hatch (dph) striped trumpeter
larvae. In both the rotifer and Artemia challenge trials, it was determined that
Pseudoalteromonas agarivorans ST18 and Aliivibrio fischeri ST7 had the
least negative effect on rotifer and Artemia survival numbers. To further
assess the probiotic capability of strains ST18 and ST7 rotifer and Artemia
cultures were challenged with pathogenic strain Vibrio proteolyticus V760
mixed with strains S118 or ST7. Strain ST18 was found to have a probiotic
effect in that cultures containing both V760 and 5T18 were not significantly
different from the controls but produced significantly better survival compared
to the pathogen-only treatments.
To further investigate ST18 and ST7 probiotic capability, they were added to
striped trumpeter larvae cultures either directly through addition to water or
through bioencapsulation in live fed rotifers. TRFLP was used to monitor the
change in bacterial community and to track individual probionts by detection
of unique terminal restriction fragments (TRF). The addition of strain ST7
alone was found to be disadvantageous to the culturing of striped trumpeter
yolk sac larvae, while the addition of strain 5T18 and a combination of
strains 5T18 with ST7 showed no significant reduction in survival. Tracking
of strain ST18 using TRFLP was successful with the strain specifically
detected in treatments where it was added by both bioencapsulation and
direct addition.

Item Type: Thesis - Research Master
Authors/Creators:De'Pannone, MV
Copyright Holders: The Author
Copyright Information:

Copyright 2010 the author

Additional Information:

Thesis (MAppScAqua)--University of Tasmania, 2010. Includes bibliographical references

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